[sciboy]

Honestly, the only way to understand regression is to study something like Mccullagh & Nelders book. Anything else and you are going to have a very hard time really being useful without misinterpreting the results. There are some real subtleties to interpretation of regression coefficients, and more importantly structuring your data in such a way that you will answer the questions you want.

It's not an easy book, but if you've gone through to at least third year level in statistics it's approachable and you will understand it to a deep level.