When I tried to play Toribash( I had 2.4, and got 3.0) I found that if I run my mouse over a muscle to select it, imediately after it would highlight, the mouse would move the the exact middle of the screen, it might be from fullscreen mode, but I don't knw.
In the older Toribash, I played it in fullscreen all the time, and nothing like this happened.

I have an emac 10.4.10, 1GHz Power PC G4.

Really excited to pay, but if this can't get sorted out, then I'll have to sob in a corner for a while.

It may be your mouse. (not saying it is) Try changing settings, cleaning it, getting a mousepad ect.

Also, try it on windowed mode, and see if that's the problem.