I recently installed Kubuntu 8.04 on an external USB hard drive... all self contained. I can go to any PC, hit F-whatever for the boot menu, and boot right to my external hard drive.

However, the hard drive doesn't show up when I plug it into a Mac and hit "Option" for the boot options. I have a MacBook Intel Core 2 Duo with Mac OS X 10.4.11.

Any ideas? I'd like to make minimal changes to the Mac (otherwise it would defeat the point of my self-contained Linux install)