@zaphee- you dual boot the iPod by using the hold button when the iPod turns on, with the apple logo.
And if you just want Rockbox as a custom firmware for your iPod to allow for more features and games and for a wider range of music formats, then i would not recommend installing iPodLinux. As it is a pain in the a** to install (takes a lot of time, and usually requires partitioning your iPod). It also has like no support and is pretty much a fallen project where their devolopers lost interest and it still has a lot bugs that need to be worked out. And alot of their games run at bery low speeds, some dont even run at all!
And you can just install their bootloader and not iPod linux, but as this is a Rockbox forum and not a iL forum like Llorean metioned, so dont ask for help with installing their bootloader here.