hi
the first bit is true, there are some linux varieties made for PPC processors. Ubuntu linux is one, YellowDog is another, I believe there is a Fedora Core variety for PPC as well.
Don't tell anyone, but if you aim to use Firefox and Openoffice.org, they will be faster on Ubuntulinux for the PPC than they are on OS X.
As for running Linux on a MacIntel, I cannot tell for sure, since I don't have one, but I understand that you need Apple's bootcamp installed first and only then you can use a normal Linux installer in order to have a menu for picking your operating system when you boot up your computer.