You can't break anything, why don't you try it?
Probably will. It boots on a 6 year old PC, so I don't see why not.
Yeah, but the question was if it will boot an iMac,
and I doubt it, since Knoppix system requirements is Intel Processor i486 and above.
(Unless you have an iMac with an Intel processor)
If your iMac can run Mac OSes (eg. Mac OS X) then you need a PowerPC (PPC) version of knoppix. It looks like you could download a PPC version here: http://debian.tu-bs.de/knoppix/powerPC/
i wanted to try it out in my graphics class.. i'm pretty sure they have OSX on it