http://docs.rosink.net/imac-triple-boot.pdf
This guy claims that he installed x86_64 Linux and Win64 on his intel Core 2 Duo iMac, seems this mashine really rocks them all^^
Btw I own a Core Duo iMac and have had the following experiences with some LiveCD Linux systems. (Haven't had the courage to reformat my drive yet)
1. Ubuntu 6.06 LiveCD works fine with 1680 by 1050 resolution
2. GRML Linux 0.8 works fine and shows me the Tux twice while booting (1 Tux per Processor Core)
3. Ubuntu 6.10 LiveCD Boots but X-Server is screwed up, and so textconsole is. This is particularly interesting since the guy in the link above claims to be using Ubuntu 6.10.
I haven't tried Windows with the rest of Boot Camp yet (only installed the Firmware Update but not the BootCamp formater and guide) and probably will never try because I can't stand the idea of a Mac beeing controlled by such an inferior OS
//Edit just found a menztion of my edgy problem in the doc above, it is probably caused by compositing and or radeon driver