Using the Apple supplied Boot Camp, the open source project that came up with the first way to dual-boot an Intel-based Mac in Mac OS X or Windows XP has now provided a means of adding Linux to the mix. It is now possible to do a triple boot, and have Mac OS X, Windows XP and Linux all running on your Intel-based Mac. Instructions are on the OnMac.net Web site.
There likely isn't much business value, but it's fun that someone's doing this. The process of getting Linux running isn't for the technically faint of heart. Users first boot the Mac into Windows XP, which in turn activates other software, including the Lilo bootloader, from which they can choose to run the open source operating system.