then just buy a gtx460 you have a quad core cpu so thats a good starting point adding a decent gfx card will make your system sing. as long as you have a decent psu.
i know your gpu isnt particualry powerfull but it will be fine for most games as they often only require 2.2 to 2.4ghz dualcore cpus for minimum onf 2.0 quads for recommended.
so banging in a 460 should bring your rig to life... like fitting grannys wheel chair with a rocket motor...
it may be loude but it will put a grin on her face