I've no idea what you are playing, but very few of the games I like to play have OpenGL support, maybe Software Rendering, but that's just really not a good solution to anything. Unreal2 doesn't seem to offer OpenGL, unless it's very hidden?
Just to add, I gave the latest NVidia drivers (451.67) a try over the weekend, but quickly had to roll back to the 398.36 drivers after the problems with older DirectX games came back. So it doesn't seem this was a simple bug, but rather a change in the drivers that affects backwards compatibility.
Whilst the stuttering/pausing is now gone, I'm still left with problems where my character can suddenly "flip" direction if I'm turning too fast with the mouse, especially whilst strafing. Switching off mouse smoothing, reducing mouse sensitivity and the DPI of my mouse all help to some extent, but the problem just doesn't go away. It's really annoying in a fast-paced game like this and my system has no problems playing Unreal Tournament 2003, which uses the same game engine? Understatement that, I'm getting a smooth 200+ FPS there. Anyone able to offer any advice on this? I still managed to complete the game for the first time today despite it, but I'm hoping in future I'll be able to have a smoother experience.
Supposedly fixes the random mouse jump/spin problem. Not sure if this is the same as smoothing.