After a minute or so in-game, my desktop mouse cursor shows up locked to the center of the screen, over the crosshairs. I'm on a PowerMac G4 running OS 10.4.1, however, the issue is likely caused by my mouse, which is a Wacom Graphire 2 Tablet.

Are you running any other application in the background which might be vying for attention?

I have the same issue, G5 10.3.9, don't know what kind of mouse, and yes I usually have stuff open.

Usually this doesn't happen if you click on the vendetta window after looking at another app, as opposed to hitting command and tab.

There are other applications open, but I don't switch to them at any point.