At the Omega driver site, I read that he turns off enhanced cpu instructions in opengl, in his drivers by default. I had often thought that perhaps disabling this may eliminate any confusion that the os or the game or even the cpu was in over the use of the mmx, sse, and 3dnow instructions. I am running a xp1800 and a gf3ti200 on a nforce mobo.
I have normaly had lateral lag when moving in games, and generaly poor performance.
Once I disabled the enhanced cpu instructions, everything smoothed right out. You might want to try this for a boost.
It may help some out.