Athlon XP+ will be around for a while, with the .18 micron die (Palomino) being used probably til around 2000+ to 2200+. I believe AMD is going to introduce Thoroughbred in Q2 of 2002, which is just the Palomino core on a .13 micron process. They'll ramp the speeds on the .13 micron process until the Hammer lines (totally new 64-bit architecture) are ready for desktop use, which probably won't be late 2002 to early 2003.
You don't need any "special" cooling system, just a heat sink and fan. Now, the price and cooling attributes of these heat sink/fan combos vary greatly, but thats a whole nother story. Check out the cases/cooling forum for some people's inputs.
Chiz