Mouse lag? How to get rid of it?

[brontosaurus]

I just got the game of the year edition on steam and want to see what all the hype about this game is... Only problem is, there is absolutely horrendous mouse acceleration. I can't play an FPS game with it on. Is there any way to disable? I've heard about the directinput fix, but not being able to use a mouse for menus is a huge NO for me...