I was having a mouse lag issue in Dead Space, and I followed the useful instructions here which completely solved that problem.
It introduced another problem, however, which is that the mouse sensitivity is very, very low even when the sensitivity bar in the options is turned all the way up. Luckily I have an expensive gaming mouse and I can increase the sensitivity on the mouse to make it playable, but it's still too low even after doing that. When I right click to aim, sweeping the mouse over a foot turns the view about 30 degrees.
It's more playable than it was with the mouse lag, but this is a problem too. Is there any way to remove mouse lag but still have reasonably high sensitivity?