Will Sowerbutts has published an article about installing Debian GNU/Linux on the Mac Mini
Apple's Mac Mini is something which a lot of Linux users have been waiting for: An inexpensive, readily available PowerPC system in a small, quiet and attractive chassis.Read more
Debian is very popular on Intel i386 compatible systems. Due to the open source nature of the Linux kernel and the Debian operating system, it is possible to build the same software to run on the PowerPC processor found inside the Mac Mini. It's simple to swap your big, noisy old PC for the slim, svelte Mac Mini, and this page aims to show you how to do just this.
Personally, I bought the Mac Mini as a replacement for my girlfriend's aging 1GHz Pentium-III system. Thanks to the portability of Debian and its advanced package management tools, making her new Mac look like her old PC took only an hour or so.