I'm going to do this with Skye so I've read up on it...

First you need to have your CGC...the testing information and requirments are found here:

http://www.akc.org/events/cgc/training_testing.cfm

Then for the therapy test, it's basically the same test, but with some added medical equipment tests and such:

http://www.tdi-dog.org/tditesting.html

This website is from Therapy Dogs International. I know that Amy (Cincy'sMom) does therapy with her dogs so she will know a little more about the testing. I'm not absolutely sure if you must have the CGC before you test, but that is the way my training school does it, so that's just what I assume!

Good Luck! Therapy can be extremely rewarding for both the dog and the owner!!