Haven't (yet) tried installing Linux on an Amiga, but I have used Linux for a very long time (I began using Linux back at kernel 0.97 on my shiny new 386SX). A major factor in installing any form of Linux is the distribution you choose. If you get one that's put together well, it can be as easy as popping a CD in and clicking a few buttons... or it can be a hardcore intense series of bootstrapping and compiling programs. Google and find what distributions exist for Amiga. That should be your first step!
Of course, the more Unix knowledge you have, the better.