I had a problem with a 'falling cursor' that loved the bottom of the screen. I've had this problem in a few games. Usually, I use the keyboard to navigate to 'options' and then 'roll' the mouse and randomly click to try to hit the 'use' button. After that the mouse moved freely, but would be 'broken' again the next time I ran the game. However, I finally found a permanent fix to this problem. To fix this problem I set the game resolution to the exact resolution on my iMac.
I went to the Apple Symbol in the top left corner and clicked on 'About This Mac'. I then clicked on 'More Info' and Graphics/Displays. I then tried to find my iMac Display resolution in the options menu. I eventually selected 2560 x 1440.
STALKER now plays in fullscreen with no mouse troubles.
I've got an iMac 11,3
Intel Core i7
2.93 ghz Quadcore
8gb Ram
ATI Radeon HD 5750
Mac OS X 10.6.5
I have added this to the tips and tricks section.