Mouse Shynanigans

Ok, I started with a windows machine and eventually switched to a 17"pb(wich I love). One thing that has majorly bothered me has been the difference in mouse feel and reaction to movement in comparison to my older windows machine. The reason I know that it is not the mouse is because I have tried my windows mouse and a new apple bt mouse to see if the results were still the same. With the two mouses I have tried on the apple it feels like there is less sensativity, if you will. I know how to change sensitivity on the mac and when I do it does speed up and become more sensative but in small little movements it stays the same. Like if I were to put the mouse in the middle of the screen and move it a small small amount it wolnt even move, but on my windows machine it could sense those small small movement. This problem is kind of hard to explain but somewhat frustrating with my everyday use. I hope their is some kind of setting that I can change to fix this. Thanks.