(FORTUNE Small Business) – When my father graduated from high school in the 1960s, he spent a summer hitchhiking through Europe, holding out a U.S. flag and his thumb and working his way around the Continent. Given that hitchhiking's not really an option anymore (at least, according to my father, it's not an option for me), the most common way to get from one European city to another has recently been by rail. But unless you're on a leisurely three-month tour, the trains can be maddeningly slow. A trip from, say, Barcelona to Amsterdam, takes more than 15 rumbling hours and crosses four borders (with a passport check at each one). And it's not cheap: The fare runs about $390. However, there's a better way. I recently made that same trip, Barcelona to Amsterdam, on a discount plane ticket that cost less than $150 and took just two hours.

Call it the Southwest effect. Beginning in the mid-1990s, when the European Union deregulated air travel, a number of upstart airlines started providing no-frills transport around Europe. The airlines--Ryanair, easyJet, buzz, and bmibaby, among others--are now fighting to get established, mainly by offering travelers some very sweet deals. When Ryanair launched its website in 2000, it listed roundtrip fares between Glasgow and London for [euro]1 (that's about $1.50). This past summer, to celebrate both Ireland and Germany qualifying for the second round of the World Cup, Ryanair gave away 6,000 free seats on all routes to and from Germany. And easyJet? When a competitor entered the London market, easyJet employees boarded the rival's first flight wearing orange jumpsuits and handing out free tickets.

Even excluding such special promotions, the average fares on the carriers are surprisingly low: about $50 each way on Ryanair and about $80 each way on easyJet. I found a ticket from London to Dublin for just $36, including all fees and taxes--less than it cost me to get to the airport. Many of the fares are hardly enough to cover the airlines' cost of operation, but the carriers are trying to make up the difference through commissions when people book a car or a hotel on their website (about one in three European travelers does). The carriers also save by flying a single type of aircraft--often a Boeing 737, with six seats in each row and a single aisle down the middle--and they use smaller airports, which host them on the cheap, sometimes even for free. In a decided inconvenience, some of the airports are somewhat outside the city centers. (Ryanair, for example, advertises Frankfurt as a destination, when in fact the airport is at Hahn, about 60 miles from the city.)

As in the U.S., discount airlines have been thriving, despite a brutal travel recession. The global airline industry lost about $18 billion in 2001, according to the International Air Transport Association--the worst loss in the history of air travel--and carriers like Swissair and Sabena have filed for bankruptcy. But Ryanair actually beat analysts' expectations for the last fiscal year, with profits up 44% and traffic up 38%, to 11 million passengers. Ryanair plans to acquire as many as 150 new Boeing 737s between 2002 and 2010, which would give it the largest--and youngest--fleet in Europe. And because the discount airlines use newer planes, they tend to have better on-time records than the biggies. According to one survey, 75% of easyJet's flights in a given week landed on time, and 93% landed within an hour of their scheduled time.

So if you're heading to Europe and want to see more than one city, flying is definitely your best option. But because the airlines are so new, there isn't a lot of information for U.S. travelers about how best to navigate them. Here's what you need to know:

DON'T EXPECT TO FIND ANY OF THESE FLIGHTS THROUGH U.S. TRAVEL AGENTS. I wanted to book a madcap trip that would let me try out as many airlines as I could, flying from London to Barcelona, Amsterdam, and Dublin in just four days, but most travel agents here tried to talk me out of it. (One who considers herself an expert in European travel added that I was out of my mind.) Why the resistance? U.S. agents don't get a commission on those flights, so they're not listed on booking software systems like Sabre and Apollo. They also aren't listed on consumer websites like Travelocity or Expedia. easyJet once painted the motto "Cut out the middleman" on one of its planes, but since travel agents are the middlemen in question, they're not all that eager to speed the process along.

The best way to find a ticket is by looking at the European websites that specialize in European discount travel (see "How to Book"). I found all my flights through applefares.com. Curiously enough, that site is compiled not by a travel professional but rather by a dedicated hobbyist--Darragh Smyth, an Irish budget traveler who works in the biology department at Oxford University. Smyth's site is accurate and easy to use, and it's worth noting that you buy tickets only from the airlines themselves, not from sites like these, so you don't have to worry about giving your credit card number to a stranger.

When you're ready to book, realize that the airlines offer phone reservations but don't have U.S.-based 800 numbers, so the calls can get expensive, particularly if you get put on hold. A better bet is to book online, where you often receive a [pound]5 discount (about $7.50).

EXPECT TO PAY EXTRA TAXES AND FEES, WHICH ARE SOMETIMES MORE THAN THE TICKET. In some cases the extras are insignificant--my flight from Barcelona to Amsterdam cost about $122, with another $8 in fees--but it's more commonly a bigger fraction of the total. Amsterdam to London's Heathrow on BMI ran $35, with another $20 in add-on charges. These cover things like landing fees at specific airports, so there's no way to predict how much you'll have to tack on. Also, they don't show up when you're browsing, only when you indicate that you're ready to purchase tickets. And if you're paying with a credit card, you'll probably get hit with one final surcharge of several dollars, depending on which airline you're flying.

PLAN ON USING LONDON AS A HUB. Most flights originate there, though they rarely use Heathrow, where the gate fees can be steep. Instead, bmibaby leaves from East Midlands, about an hour and a half outside London, easyJet flies out of Luton, a smaller airport 30 miles from the city, and most of the Ryanair and buzz flights leave from Stansted, another small airport nearby.

DON'T EXPECT TO BE PAMPERED. These are bare-bones operations with all conveniences sacked for savings. That means no in-flight meal, and no peanuts (though in most cases the flight attendants push around a snack cart and let you buy orange juice and cookies. On one easyJet flight, I spent $5 on a cheese-and-pickle sandwich, which tasted about as good as you'd imagine).

You also won't get any entertainment--aside from wisecracks from the crew--and no frequent-flier miles or seat assignments. I heard one story of a passenger actually having to load his own bags on the plane. Perhaps the biggest caution: no refunds. If a flight is canceled and it's the airline's fault, you'll most likely get your money back for the ticket, but don't expect any money for meals or accommodations.

LEAVE THE STEAMER TRUNK AT HOME. Most of these airlines will weigh both your checked baggage and your carry-on. Checked items on easyJet, for example, are limited to 25 kilograms (about 55 pounds), which should be enough for most people, and carry-ons are capped at five kilograms (11 pounds). You'll be charged for every kilogram over that.

SHOW UP ON TIME. Because the airlines' operations are so lean, they try to keep the planes in the air as much as possible. That means they won't hold a departure even a few minutes for the occasional laggard. Ryanair's boarding pass reads "Don't be late to the gate." easyJet tells passengers, "If you're late, we don't wait." On one of my flights, a passenger who missed the boarding call almost had her luggage taken off the plane. "We are locating her bags, and she may not be able to join us--whatever," the captain announced blithely. (She finally showed up a few minutes later.)

Earlier this year some of the airlines came under fire when pilots were accused of rushing air traffic control procedures to meet their tight schedules. And on the ground, the typical turnaround time is just 25 minutes between landing and takeoff. While that kind of rush might sound appealing compared with sometimes sluggish U.S. carriers, 25 minutes isn't enough time for a crew to clean the airplanes--or the bathrooms.

Which leads us to ... DON'T EXPECT STATELY TRAVEL. All easyJet employees are required to dress in a loud shade of orange: orange shirts, orange hair bands, black slacks with an orange label. The planes and even the trash bags are orange. It gives a kind of theme-park atmosphere to the flights, but as branding, it's strangely effective.

Other flight crews are a little less fun and a little more businesslike. On my Ryanair trip to Dublin, a flight attendant giving the safety demonstration accidentally hit me with a life preserver, whacked the head of a passenger in front of me with the seatbelt, and then berated him for talking during her presentation. "They don't pay them to smile," the man sitting next to me said.

Despite those caveats, the main thing to remember is this--for getting around Europe, discount airlines may not represent first-class travel, but they're faster than other modes of transportation and cheaper than other airlines. On that slightly traumatic Ryanair flight, I paid only $36 for my ticket, and we landed in Dublin ten minutes ahead of schedule. That's a combination even my hitchhiking father can understand.