Help me choose a computer so I can start pwning :)

[Gypsy]

Hmm, I had written a reply with the problem I have with my current computer but it's not showing? It freezes about 30 seconds after booting. The mouse curser stays stuck like it's trying to load a program. I've tried running it through the bios and it goes through a really long process of repairing itself until it just kinda craps out. Sigh.
Anyways, if I have to get a new one I'd like to keep it around $500 or less.
Thanks for all the help so far, ya'll are awesome.