Mouse lag

[LeakingBlood]

I just purchased this game from Steam to play and found that I can't move the mouse around properly.

The graphics including the opening cinematic upon starting a new game plays out properly and frames per second are fine all on settings. However, any mouse movement freezes the game for a second before looking in the direction I want.

I've updated my drivers only to come to the same result. Any fix for this?

I'm playing on an Asus N61J, Core i7, 4 GB RAM, ATI Mobility Radeon HD 5730.