Thanks, Cory!
Yeah, the Power Computing machine works fine, except the red and the blue are backwards for some reason. I don't know whether it's some sort of setting that I've missed, or if the video card has gone south. Other than the strange looking graphics, it seems to be working fine, now that I've replaced the fan in the power supply, which had the worse case of blown bearing I've ever seen on a computer fan.
The 7100/66av works fine, too. I upgraded it from 16 MB to 72 MB of memory (4 16MB sticks, and there appears to be 8 MB on the board?) The 700 MB HDD was completely dead, but I installed a 1 GB drive and it's working fine. I installed System 8.6 on it last night.