So he tried using the "Guest" account. At first that didn't work, but that turned out to be because he'd renamed the files and left off the .avi extension. Then he installed the software and as I watched, I saw a part where it asked if he wanted to have a program called 3ivx become the default. I knew I'd said no when I set up my camera, but I seemed to recall saying yes when I installed his. So I had him say no on the guest account. The software/camera interface ran just fine, he uploaded his movies, I quit trying too fix his account and we went to bed.
This morning I went in and renamed the 3ivx file in his account. This allowed me to remove his Quicktime program (which I'd been locked out of) from the dock. I then reinstalled his Quicktime. This allowed me to reload the camera software (which I'd also been locked out of) and when it asked about making 3ivx the default I said no. Then I plugged in the camera and voilà! everything worked as planned.
I get major credit for not throwing the Mac out the window last night.