I have seen the light.
1.4 TBird, not OC'd
GF3 (stock, non-Ti model)
First, I recommend setting texture detail to normal. Yes, normal. It runs better if you don't have that 128 megs of ram that the ******* GF4 users have.
Next... this will sound crazy, I know... disable the pagefile. Yes, disable it.
See, the difference between D3D and OGL is this...
D3D: slower, but more inclined to be smooth
OGL: WAY faster, but can get jittery like a small child that found your crack stash
Now, if you watch OGL normally, you'll see that when it pauses, the HD light goes on. It's because WinXP always uses a bit of the pagefile, so kill it dead. (don't do this in Win9x. it causes explosive diarrhea for your computer. not pretty..)
Turn off VSync.
Watch the Magic.