Get yourself an AGP graphics card with either GForce or Radeon chipset with at least 128mb ram (NewEgg has a decent 256mb one for under $100).
I'd go with at minimum an 80GB hard disk at 7200RPM (if you're serious about gaming then NOTHING under 7200RPM!).
Ram, at least a gig; processor, at least a 2.0ghz or equivelant (Myself I prefer the AMD Athlon 3200 and above).
Newegg will have the cheaper prices 90% of the time; plus the rate that they get shit out to you is well worth the $10 you could save shopping anywhere else.