I would get another Gig of ram first, and dedicate as much as the bios will allow to video.
Get latest drivers for on-board sound, and turn sound acceleration down one notch on the slider in windows audio properties.
Be sure to turn off 3d sound in game.
Set a static swap file as large as you can.
Disable all un-necessary processess and services set to run at start-up, including AV and printer software.
Fresh boot and try again while shopping for new vid and sound cards.
