personally i use an AMD sempron 2400+ (older but surprisingly still runs latest games very strongly) with a gigabyte.... kvm-700 i think it is mother board (2004 RZ)
only 512 mb ram (DDR) and a 256 mb Radeon from a seperate company.

All in all i can still play nfs most wanted at perfect frame rate graphics very close to top.

so far the only game to get close to unplayable is morrowind oblivion and seeing the list of games you want. my brother plays the same ones and does fine on this system, should cost around... 450 (aus dollars not sure what your currency would be)

Hope i was in some way helpful