I'm trying to install Debian Wheezy on one of the earlier Intel based Mac Minis. I first tried pressing "C" a non-Mac keyboard, but that just didn't work! Then I tried asking the system settings to boot off of the foreign operating system CD, but that didn't work either - I guess I burned a amd64 version of Wheezy by accident...
Unfortunately, the system would not boot off the hard drive again. At least I was able to eject the CD by holding down the left mouse button upon boot. Still, I was presented with the "No Operating System Found" error.
Finally I figured I would try a real Mac keyboard. Wow - that worked! I was able to choose which OS by holding down the option key.
Now I'm using "diskutil" to resize the volume so I can have at least 10GB of space to work with. I may end up removing Mac OS altogether, even.
Actually, I'm running squeeze, and I like it because its super stable.