I'd recommend:

AMD Barton XP2500+ CPU $265
Asus A7N8x-DX $210
512 MB DDR 333 $90

Prices are in canadian dollars (divide by about 1.5) from our local computer store.

Edit: oh, this is assuming it's for a desktop/workstation. If you are looking for a server, that would be different.

Cheers,

Alex
--
Gossamer Threads Inc.