the 166MHz FSB version of the Athlon XP is coming out in a few months (i think), maybe it's best to wait for that. Or better yet, wait till next year.... by then you could get a ClawHammer :P
Athlon XP 2200+ and above is the best choice as of now, it has the newer codename b/c of its smaller .13 core.
For Mobos, you can't go wrong with ASUS or GIGABYTE.