Great questions.

A good European-based team should have a few different kinds of riders. There are:

Classics riders- They are great in one day events, generally can produce mucho power and sustain it and then still pack a punch at the end. They don't necessarily climb well enough to be Grand Tour contenders though. They tend to be built larger and stronger. Johan Museeuw, George Hincapie, Andrea Tafi...

Grand Tour contenders (called G.C. riders, which stands for "general classification" and refers to riding for an over-all position in a longer event). These are guys that can Time Trial and climb well enough to always be near the front and compete in an event that stretches from ten to 21 stages. Lance Armstrong, Jan Ullrich, Joseba Beloki...

Climbers- Tend to be small framed, light and have huge aerobic capacity. Generally don't time trial well enough to win a Grand Tour, such as the Tour de France, but they can finish well enough in the mountain stages (even winning stages) that they can finish in the top ten over-all. Richard Virenque, for example, won a brilliant stage in the Tour de France last year, on the Mont Ventoux, but he can't win the event over-all.

Sprinters: Usually hide in the pack until the end and are escorted towards the finish by their team. The team accelerates the pack so that nobody can attack off the front and "leads out" their man. They stay in a line and drive the pace until they can no longer hold the speed, then they peel off and let the next guy in line work. Ideally the last guy is pulling over at about 200 meters to go, leaving the team's sprinter to go like hell to the line.

You will also hear the term, "domestiques" used a lot. These are guys who are paid to work for the stars. They break the wind for long periods. They go back to the team car for water bottles to bring up to the stars. If the star gets a flat, they will give him their wheel if the team car isn't immediately available. They are brilliant riders, in their own right, but just lack that little something extra...U.S. Postal's riders in the Tour de France are virtually all riding as domestiques, with the lone objective being getting Lance to Paris in yellow.

Hope this helps. If you want more info, just ask. It's the only way to learn.