The school is in the back opposite where the Reclining Buddha is (if you facing the entrance to the Reclining Buddha and turn around you'll be facing the school but you have to either walk around or though the courtyard). From the front gate the Reclining Buddha is to the right and if you go around to the left after you enter along the outside wall you'll run into the school. There may be an entrance on that side for students but we were just walking around so I can't really say. I pretty sure you'd get a student pass or get taught the secret handshake if you take a course.
Edit: The student entrance is outside. If your at the main gate don't go in go to the left around the outside and there will be a building with a dull green sun shade on it That says WAT PO Traditional massage in white letters.
The school's contact information is as follows:
Wat Po Thai Traditional Medical School
2 Sanamchai Road, Wat Po, Tatian
Bangkok 10200 Thailand.
Tel. (from overseas) +66 2 221-2974 or +66 2 622-1687
Fax. (from overseas) +66 2 225-4771
Email: WatPoTTM@netscape.net
or see
http://www.watpomassage.com/2008/
There are several locations outside of the temple (see the website above). A 30 hour general course is 8500 baht, 12,000 Baht for Advanced Thai Massage, 6500 Baht for Foot Massage, 6500 Baht for Oil and Aroma Course, 5000 Baht for Infant and Child Massage Course)
Here are some helpful tips to get good training at Wat Pho Massage School:
1. The certificate you receive at the successful completion of a class does not replace the training required in your country.
2. Register on the day you wish to start the course (around 8 - 8:30 a.m.)
3. Pay in cash