Ah well, time moves on past us and our equipment. There's also another problem with installing recent operating systems on the Mini -- it won't read the DVD. One has to hook up an external optical drive.
I'll be retiring the Mini soon, not because it won't run more advanced versions of OSX, but because the sound is failing. Not a peep through the headphone jack, and the speakers are gradually fading out too.
Allan, if you're still reading this very old thread, I encourage you to try the latest Folding@Home client on that powerful desktop. It's too nice a machine to sit idle!