Roel,
I'm not really sure if thats useful right now, Windows XP doesn't support 64-bits CPU's yet as far as I know, but if the Athlon 64 is much faster than the Athlon XP (in 32-bit mode), I think it would be an option, but the prices are high, but then again if its worth the money I'll probably buy one.
How about the Athlon 64 3000 "Newcastle", at least I can afford that one, the Clawhammers (Athlon 64 3200) are way to expensive...

.
Thanx,
Greetz

,
Marcel