Learning Regular Expressions is like learning another language.
I have found learning it is easier if you go step by step.
The best way is to read a few explanations and choose the one that seems to be most understandable to your.
The easiest one I found was the manual for TextWrangler. Chapter 8 explains writing search and replacement expressions. (you don't have to have TextWrangler to get something from this part of the manual).
You can download the manual here:
http://pine.barebones.com/manual/Tex...ser_Manual.pdf
Rock on.
Archon