I'm running Crossover Games 9.0
OS X 10.6.3.
Intel Core 2 Duo 2.16 ghz
Nvidia GeForce 7300 GT with 128 mb VRAM
I'm playing the Steam version of Deus Ex Game of the Year edition.
At first, my mouse was stuck at the top. After trying a few different resolutions (none of which were my Mac Resolution, and none of which worked), the game at one point crashed and gave me the lucky opportunity to run in safe mode, optimize the video, etc.
One thing you might do is delete local content and reinstall.
I allowed Deus Ex to detect my system setting, and then I opened it in safe mode, and to be honest, I'm not entirely sure which one did the trick, but the mouse works and the game plays beautifully.
I'll keep an eye here from time to time, and if you have the same problem, I'll at least take a shot at walking you through the settings until we find out what works.