What kind of mouse are you using-wired or wireless? What kind of surface are you using it on?
I have the Apple wired mouse and had a tracking problem. I was using it on a dark wood desk. I resolved it by creating a "mouse pad" by taping a couple sheets of white copier paper to a spot on the desk. I have to change the paper every so often because it gets dark spots that seem to make tracking more difficult.iMAC 3.06 Core 2 Duo, 27" Screen, Mac OS X (10.6.7), 8GB RAM, Wired Keyboard, LaCie "Rugged" External Hard Drive