i'd love to have Lucky certified as a therapy dog but i could imagine her getting of the leash and jumping onto each and every bed greating the old folks with a wet kiss to the face
also, here's an answer to this similar question that a professional dog trainer gave on yahoo answers;
The two main organizations that certify you are TDI and Delta. Therapy Dogs International and Delta Society.
The tests are similar. You need to complete a course with a trainer or through a textbook and mail things in. Then you take the test. The The Delta test has two parts. The first part is EXACTLY the same as the CGC (Canine Good Citizen test) given by the AKC. So preparing for and taking the CGC will give you a good idea of what to expect on the therapy dog test.
The CGC tests your dog on basic commands, meeting strangers, being handled by strangers, and meeting another dog. Things like sitting politely for petting, sitting politely for brushing, and heeling with you through an obstacle course. Your dog can't get over-excited, and definitely can't show aggression.
The Delta test is a little more in-depth, but builds on the skills needed for the CGC. For example, your dog has to allow someone to hug him. This is an unnatural thing for a dog, and some dogs won't like it. Some dogs will snap or bite you. Your dog has to demonstrate that he won't do that! Delta test also tests your dog around medical equipment such as wheel chairs or walkers, around infirm people, around people having an argument, around loud noises. Your dog has to demonstrate confidence around these situations, and be under control. For instance, your dog may be lightly bumped by a walker. Your dog can't snap or become too upset.
Above all, these tests want to see that you and your dog work as a team. Some of the things described may seem easy to you, and some may not. Enrolling in a class will help you with your weak areas, and help prepare you for the test.
Contact your local kennel club to find out about what group (TDI or DELTA) is active near you.
http://www.deltasociety.org/
http://www.tdi-dog.org/