I guess the next steps depend a lot on your software skills. Generally speaking, knowing how to program in C and assembler are a good starting point. There is one port that was done by somebody claiming to have no previous software experience but it was not pretty. Regardless, it will likely be a lot of work.
Having said that, the first step is to familiarize yourself with the information here :
For Developers . Some of it is a bit old and out of date - there is unfortunately no "CHDK Porting for Dummies" quide - you just have to work through it and that's where having previous software development experience really helps. The biggest changes from the information on that wiki page is probably the development of code_gen and the latest sig-finder which make much of the tedious manual code creation process much easier that when that documentation was written.
If you decide to take this on, you will get lots of help here and/or the CHDK IRC channel ( evenings North America time are best). I think there is a high level list of the general steps somewhere - I'll see if I can find it.
