I'd suggest maybe getting one with Athlon 64 chip because it's more future compatible than the P4. And maybe a motherboard that supports PCi Express rather than AGP graphics, again due to future compatibility.
But i guess if you're not planning on upgrading it, or if you're not going to have it when a 64bit OS comes around, neither of these really apply. Might want to think about it.
Nice PC all in.