(FORTUNE Magazine) – ARE YOU sure you want a billion? Before you answer, consider H. Ross Perot. He has nearly three of them. He also has an original of the Magna Carta, some Remington and Charlie Russell bronzes, and Gilbert Stuart's portrait of George Washington. But what he needs is a good pump repairman. When Perot spoke recently to students at the Harvard business school, he warned them: ''Guys, just remember, if you get real lucky, if you make a lot of money, if you go out and buy a lot of stuff -- it's gonna break. You got your biggest, fanciest mansion in the world. It has air conditioning. It's got a pool. Just think of all the pumps that are going to go out. Or go to a yacht basin any place in the world. Nobody is smiling, and I'll tell you why: Something broke that morning. The generator's out; the microwave oven doesn't work; the captain's gay; the cook's quit. Things just don't mean happiness.'' What does? For many self-made billionaires happiness means work. Perot, with son Ross Jr., is bringing free enterprise to the airport business by helping to build one outside Fort Worth. Most billionaires still ply the trades that made them rich, and most discover that making all that money is a more durable source of happiness than spending it. Says Warren Buffett, who still puts in ten-hour days despite his $3.6 billion: ''I'm doing what I would most like to be doing in the world, and I have been since I was 20.'' What keeps him going, he says, is the admiration he holds for his business colleagues. ''I choose to work with every single person I work with. That ends up being the most important factor. I don't interact with people I don't like or admire. That's the key. It's like marrying.''

William Gates III could have retired before he turned 30. When the first PC was just a gleam in IBM's blue eye, Bill Gates, at age 13, had taught himself computer programming. By 19, he had founded Microsoft, the company that turned ''software'' into a household word. Money didn't drive Gates then and it doesn't now. ''Bill's original vision,'' says Microsoft senior vice president Steve Ballmer, ''was that you should be able to put a personal computer on every desk and in every home. If somebody back then had bothered to run the numbers on that proposition, it obviously would have looked like a very big business. But we never ran the numbers.'' For 1988 the numbers showed Microsoft's net revenues at close to $600 million. Gates still stays at the office some days until midnight. High tech and investing have an aura of excitement and sex appeal. But billionaires hoeing far less glamorous rows keep right on hoeing: Rudolf Oetker makes baking powder. Max Schachenmann originally got rich by producing the ''finest putty available.'' Samuel LeFrak, building a city on New Jersey's shore, has specialized in middle-class housing described as solid -- ''with kitchens and plumbing you could take to the bank.'' Grete Schickedanz, owner of Europe's largest mail-order catalogue business, still occasionally picks the fashions hausfraus will be wearing next season. Ronald Perelman has had to digest a Whitman's sampler of commonplace businesses to get his billion: perfumes, razor blades, licorice, and cigars. And Korean-born Kenkichi Nakajima, after coming to Japan as a student and being put to work in a defense factory during World War II, decided in 1949 that he wanted to manufacture a product completely unrelated to war. He chose pachinko machines, Japan's version of pinball, naming his company Heiwa, or ''peace.'' By beating swords into pinballs he has become the world's biggest manufacturer of such machines, scoring $360 million in sales last year. Heiwa stock began trading publicly in Japan a year ago; it rose nearly 70% in value the first day it was offered and is now up another 30%. The problem with working, however, is that it leads, inevitably, to the accumulation of more things -- more leaky yachts, more busted pumps. But there is a way out, elegant in its simplicity: Give money away. If fortune becomes oppressive, show it the door. Ross Perot, in philanthropy as in his business ventures, insists on strict accountability: ''I am dead interested in seeing that they deliver the goods. That is one of the reasons we give a great deal of money to the Salvation Army, because they feed the poor, they don't write books about it.'' Waldemar Nielsen, an expert on foundations and author of The Golden Donors, expects big things from Perot's foundation: ''He seems to have strong impulses and a lot of daring. Of the present crop of billionaires, he's one of the few with the potential to become a Carnegie.'' The beneficiaries of Perot's largess have been the Dallas Symphony, the Texas public schools, and a major Dallas medical center. Giving one's entire fortune away -- without wincing -- is the ultimate way of saying, ''I didn't do it for the money.'' Earlier this year David Packard announced that he would be giving nearly all his Hewlett-Packard stock, worth more than $2 billion, to his foundation, which champions causes he and his late wife believed in, such as reducing infant mortality. The size of his gift seems all the more extraordinary when one considers that the very rich, as a group, are not especially generous: Total giving seldom rises above a few percent of their net worth, at least before their death. Though the number of foundations has grown 20% since 1981, the number created by persons of great wealth has been in decline since 1969, when legal changes reduced the tax benefits. Packard will help select the organizations that will benefit from his money. But other donors choose to leave that to hired hands. Says Nielsen: ''A lot of them don't know what the hell they want to do with their money. If a man has any real charitable or intellectual causes, of course, he would give to those specific things. But a high proportion of people who succeed financially have no interest in charity, no causes, no clear-cut interests. There are wonderful exceptions, but on the whole their lives are their businesses.'' When philanthropy marries eccentricity, whimsical gifts result. Robert Lacey, a biographer of the Ford family, believes Henry I created historic Greenfield Village so he could have a place to square-dance. In old age, the carmaker became preternaturally fond of Turkey in the Straw, and retained a staff of fiddlers so he could hear it on demand. He began collecting things from his childhood -- steam irons, plows, threshers, and stoves. He captured his friend Thomas Edison's dying breath in a bottle. Though collecting industrial artifacts is accepted practice today, in the 1930s it seemed kind of loopy. Ford's hoard of keepsakes became the Henry Ford Museum. (Josephine Ford today upholds her family's reputation for whimsy by occasionally hiding live lobsters in her children's beds.)

While no current billionaire rivals Ford for eccentricity, some have definite notions about giving. Master builder LeFrak has given to so many educational institutions that he has trouble remembering them all: the gymnasium at Amherst, a library at Oxford, and an endowed chair at the University of Maryland. ''But actually,'' says LeFrak, warming to his subject, ''what I am is an explorer.'' His money is helping finance a search in Tanzania for the missing link. If LeFrak has his way, it won't be missing much longer. A few years ago LeFrak helped Robert Ballard locate the Titanic. The challenge of finding an older vessel now confronts him -- Noah's ark: ''I just received from Texas, from Jim Irwin you know, the astronaut -- a letter saying that he got permission from the Turkish government, and they want to go up in a helicopter to find Noah's ark. They feel it's sitting on top of a mountain.'' Ed Bass, the environmentalist among the Texas Bass brothers, is building an ark right now on the edge of Arizona's Sonora Desert. Called Biosphere II, it's a 2 1/2-acre microcosm of the earth under glass that includes a downsize ocean, rain forest, desert, and savanna. After the necessary flora and fauna have been installed (including mosquitoes and eight people), the ecosystem will be sealed shut for two years, starting in 1990, to see whether it can sustain itself. By then Bass will have sunk some $30 million into the project. What does he hope to gain? Knowledge and profit. No one before has engineered so large an ecosystem, and if this one works, Bass's group thinks future biospheres could be sold as habitats for Mars or stressed-out Manhattanites. Maybe Noah should have charged admission. No eccentric, Warren Buffett has limited his innovations to finance. At Berkshire Hathaway, he has pioneered a novel approach to corporate giving. Every shareholder gets to direct a sum (last year it was $5 per share owned) to any charity. When it comes to personal giving, Buffett feels that picking causes is harder than picking stocks. ''In stocks, you're looking for things that are obvious and easy to do. You try to identify the one-foot bars you can step over. But when you get into the charitable arena, you are attacking problems that have been the most intractable and resistant to solution throughout history. The most important ones are all seven-foot bars.'' Population control and diffusing the nuclear threat, the two causes Buffett's foundation supports, are ''bars so high up that I can't even see 'em. Real lulus.'' Though Buffett has spent only $10 million to $15 million on these causes so far, he intends to give much more. Waldemar Nielsen thinks Buffett hasn't even warmed up yet: ''He's one of those very rare guys who is not only one hell of an entrepreneur in business, but one hell of an entrepreneur in the philanthropic field. We haven't had one in a long time.'' The Buffett Foundation will get almost all Buffett's stock when he dies. And he doesn't think giving its trustees a narrow charter would be wise: ''That's like telling them what to invest in ten years after I die. I would rather have a smart, well-intentioned, high-grade person looking at the problems of the day through eyes that are open, not through my eyes that are in a coffin. I found in running businesses that the best results come from letting high-grade people work unencumbered. Stick around. If you're young enough, you'll see how it all works out.''