VIN is for veterinarians only(but veterinary students can join).
There is VSPN.org which is the Veterinary Support Personnel Network which is for everyone else who works in the field. This in theory is open to everyone in the field. When you sign up your application has to be approved(not sure what the process entails) but apparently they take some steps to ensure that you are actually legitimately affiliated with the field.
VSPN has its own forums that are totally separate from VIN. There is still some good reading, but its generally less medically oriented.