When moving the mouse slowly, the cursor hardly moves a pixel. Also, it's really hard to explain, but it seems that when I move the mouse left, for example, the cursor sticks to that X axis and ignores movements on the Y axis, and vice versa, making it really frustrating to use the mouse.

I have the latest drivers for my mouse (R.A.T.9). I installed the patch and Hi-Res things. I disabled UAC. I used -no3d -doublebuffer.

Please, if there's any solution I missed while searching the forums, I'd be grateful for your help.

GOG support did it! :D

"Please try disabling the “enhance pointer precision” option. To do this, go to Start -> Control Panel -> Mouse -> Pointer Options, then make sure that “Enhance pointer precision” is un-checked, and click OK."

Thank you, GOG!!!