your pc is well below spec not just on the gfx. your lucky you managed to install it. but the reality is even when you upgrade the gfx you still gonna be far short of whats required to run that game...
intel celleron is the very bottom of the pile even running at 3+ghz it cant match the old pentium 4.
you have wasted your money im afraid.
if you want to play games even at entry level you will need a dual core cpu 2.4 ghz or better an nvidia 8800gt or amd 3870 or better 2+gigs of ram.
any less than that then forget playing any new game even at minimum settings.