@krisjr...Well The minimum on Radeon that i reckon would be Ati Radeon 9600Pro if ya have 7k to spare and they are not XFX brands but Powercolor,Gigabyte,MSI etc.
@tushar_novice...For ur budget u can either get a XFX Geforce FX5200 with 128 MB Vram (For 2.5k) Or the 256MB Vram Version (for 4k).This will run Doom 3 a Normal Resolutions and will be playable decently