i dont think onboard sound is the problem it used to be in the old days, most pc onboard sounds run all games admirably now.
Havent got your graphic card, but had the min ati 9600 one. The fps was awful for me but since the advent of pci-e graphic cards, agp ones have practically fell to the floor. Picked up an nvidea 7600 with 512mb ram for £90 and now I have great graphics all on high res, no lag whatsoever
I would recomend that youensure a min of 256mb on your video card if poss for trouble free viewing