(MONEY Magazine) – WITH SO MANY OF A car's vital functions controlled by microprocessors, driving a car can be a high-tech experience these days. But buying one decidedly is not. The rules of that game haven't changed much since the very first camel trader buttonholed customers at his used-oxcart lot. May the best haggler win.

Your computer can't help much once the bidding begins, but it can at least make sure you're well informed before you step through those showroom doors. At least 20 new software programs and online services have emerged to give car buyers the data they need at each of three steps in the process: choosing the right car model, selecting the best financing and getting a good deal. While none of the dozen popular products I reviewed guide you through all three steps, the right mix of online or offline sources can tell you what you need to know. It sure beats learning it from salespeople on the showroom floor.

--Selecting a model. My favorite product for this part of the process is the 1996 edition of Consumer Reports Cars CD-ROM (Creative Multimedia, $19.99). Its powerful search function lets you screen more than 200 new cars and light trucks--plus 7,100 used models--for dozens of characteristics, including exterior and interior dimensions, price, fuel economy, depreciation rate and Consumer Reports' own trademark reliability ratings.

The program also serves up plenty of useful advice, sometimes in surprisingly entertaining fashion. One interactive section helps you hone your haggling skills by pitting you against an actor playing a showroom sharpie. You respond to the "salesman's" hardball gambits, and the program reviews your performance.

This software has some maddening shortcomings, though. For instance, it fails to provide the dealers' wholesale cost--the so-called invoice price--for each model, essential knowledge for anyone bidding on a new car. Consumer Reports does have the data, but you have to call an 800 number and pay an extra $12 for the complete list. Says a Consumer Reports spokesman: "Providing that information by phone is the only way we can keep it up to date."

A close second was the Edmund's Automobile Buyer's Guides site on the World Wide Web (http://edmund.com). It lacks the screening and multimedia capabilities of the Consumer Reports CD-ROM, but it's timely (the data is updated at least every two weeks for new cars and quarterly for used cars) and free. This is the place to fill in the gaps in the Consumer Reports data, including up-to-date invoice prices for new cars and trade-in prices for used cars. I liked Edmund's Website much more than its rather slapdash CD-ROM Edmund's 1996 Buyer's Guide (Edmund Publishing, $6.95).

--Deciding whether to pay cash, borrow or lease. You'd think a computer would excel at the complicated calculation that compares leasing to conventional forms of financing. Indeed, many software programs, including Buy or Lease It (KJ Software, $12.50) and Expert Lease Pro (Chart Software, $129.95), give it a fair shot. But they fail to provide enough guidance to keep car buyers from entering faulty data, and the program's default assumptions tend to make leasing look better than it really is. For example, both packages assume that all people who lease invest the money that they would otherwise be spending on loan payments. Somehow, I doubt it.

In any event, I see no reason to spend as much as $130 on software to analyze transactions that you probably won't attempt more than once every few years. Bypass these programs, and instead use the loan/lease calculator included in the $20 Consumer Reports CD-ROM.

--Getting a good deal. Tired of the showroom runaround, growing numbers of consumers are turning to buying services. (See the March issue of MONEY, page 132.) These outfits enter into agreements with dealers to sell cars at discounted prices to the services' members. Auto-by-Tel (http://www.autobytel.com/), free on the Internet, or AutoVantage on America Online (annual membership dues: $49) are typical: You enter your address and the kind of car that you're seeking, and the computer sends you back the name of a dealer in your area who agrees to sell at a preset price.

The best of this lot is probably CarBargains on America Online (keyword: CHECKBOOK). Also accessible via phone (800-475-7283), CarBargains charges $150 to get quotes from the five participating dealers that are closest to you. (You pay by credit card online.) Because the dealers know they are competing for your business, CarBargains' quotes consistently beat those of other buying clubs. The service even comes with its own warranty: If you end up buying your car from another dealer in the same area at a lower price, CarBargains refunds your $150. The camel traders would never have dreamed of doing that.

Author of Personal Finance for Dummies (IDG Books, $16.99), Eric Tyson is a financial counselor who teaches personal finance at UC-Berkeley.