I am about 1/4 of the way through the game. I have had no problems running the game so far. Suddenly I get to a spot and the game runs super slow. My cursor jumps all over the place. There's no way in hell I can aim and actually hit anyone. The problem then continues in the menu. It took me forever to simply get my cursor to get to the save button. Anyone else encounter this problem? And any suggestions? I am running on Windows 8.

Maybe it runs better with Kentie's launcher. It's worth a try.
http://www.kentie.net/article/dxguide/

Are you using Glide (via nGlide) or DirectX? I experience slowdowns when using nGlide (everything running at 0.5 the speed it should). I disabled the Vsync in the nGlide settings and it seems to work for me.