Those are the first things I did. Right off the bat I asked them for a new mouse, then I disabled the PS/2 port in the BIOS so as to take it out of the equation.

I tried troubleshooting it again this morning. Didn't have any solid conclusions. They did have a remote control application installed called "LogMeIn," so I disabled that since they're not using it at the moment. The program had added a second display adapter of its own, which I disabled, and I unchecked the component that loads at startup via msconfig. We'll see if that has an effect.