As another Vietnam vet, I can tell you that as both Old Medic and I have said, your local VA is really quite helpful. Pappy's advice to google the VA is good too, but when you can get a local VA representative to help, you can get it done more efficiently and also more correctly for your local situation.
If you have either not been in contact with the VA prior to this or had a bad experience in the past, I can tell you that things have really changed. Also, with the exception of one guy in these forums, attitudes toward us Vietnam vets has changed a lot in the intervening years.
Tony