The Athlon 64's are supposed to be fairly overclockable.
The Athlon XP 3000+ is about equal to a 3.0GHz Pentium 4; however, the Athlon 64 3000+ is a bit faster across than the XP across the board. It is a bit confusing, that's for sure.
If you run a 64-Bit OS (like Linux, or the 64-Bit edition of Windows XP (trail version is out now), then you'll see a performance boost. How much? Well, Mandrake claims about 20%. With Windows, it'd be less, since only the OS itself is 64-bit. With Linux, all the software is also 64-bit (score one for open source! With the source code you can recompile for any CPU).
Right now the best cost/performance "combo" would appear to be this:
CPU: Athlon XP 2800+ ($121 @ newegg)
Mobo: MSI K7N2-V nForce2 400 ($57 @ newegg).
I was surprised to see an nForce2 mobo for that price! The "Ultra" version is $70. No Serial ATA on those el-cheapo boards, though. But for the system this is intended for, that's isn't too big of a deal. The Abit NF7-S is $102 and DOES have S-ATA; plus it's an Abit
Man, I'm turning into a Pentium 4 hater; before the A-64, I'd never even CONSIDER an AMD. Well, not since Thunderbirds anyway-those rocked!
Soon to be proud user of Mandrake 10 (again!). SuSE 9 sucks!