Hey all, I'm writing in to inform y'all that Knoppix runs (quite well) under Virtual PC 6 on Mac OS X.

To accomplish this,
1) Download Knoppix ISO (I used ClusterKnoppix, which also works)
2) Open the settings dialog for the Virtual Machine which you want to boot knoppix.
3) Start the virtual machine, and capture the ISO you downloaded by clicking the CD icon in the lower-left corner of the Virtual PC window (if you're in Fullscreen mode, you need to hold down the Apple key to see the icon)
4) Reboot the virtual machine, and knoppix should boot