I have built several AthlonXP computers for customers over the last 6 months and I am truely impressed.This is the best chip AMD has come out with in a long time. I build them with DDR pc2100 so far. PC2600 DDR 333 is out now, but I am not ready to jump to that platform quite yet. MSI and ASUS and ABIT and TYAN all have good Athlon XP mobos. All That I build have DVD and CD/RW and some have Raid 0+1, so i equip them with a minimum of 350 wat PS and some at 430. perormance sweet spot cost/performance wise is with a 1700+ or 1800+. The damn things are blazing fast. Hook up with XP Pro and you got the best of both worlds, hardware and OS to take advantage of it.
For a desktop system its worth the investment now. What comes out in the future will not be for consumers right away(IMHO) and will be pricey. I am looking at going with a TYAN Tiger Dual AthlonMP that has AGP 4x and 2 64 bit card slots and 4 PCI 32 bit card slots. That should provide some performance advantages, but I haven't figured out whatto put in those 64 bit slots yet. Matbe a scci card or something. New technology takes a while to catch up to manufacturer and consumer acceptance.