Is it with all games or just certain ones in particular? Perhaps check
the drive for errors (chkdsk) and run a defrag. That may help. Do you
still have virtual memory enabled? I know of some people who disable
it when they upgrade to 2 gigs of RAM thinking they don't need it
anymore (you still do).

I don't think that upgrading your mobo's BIOS would have any negative
effect.