This is an excellent gaming mouse. It can be used in either a USB or PS/2 port (unlike some gaming mice which only work in USB slots). The best thing about this mouse is the adjustable dpi levels. You can set up to 5 different speeds to be used in a game, so if you find the max dpi a bit too fast (as I did) you can drop down to any other speed that you have set.
The design of the mouse is also excellent. The buttons are positioned so that you can't accidentally press them mid-game (as I've done with a previous gaming mouse I owned).
Verdict: It's a bit expensive but if you're a heavy FPS gamer then I think this is just about the best mouse you can own. My Counter Strike kills have improved dramatically since I bought this.