If you're already an EMT-B then you should know what you need to know. You just might have to work as an EMT-B for a certain amount of time or take an anatomy course or other pre-req to be qualified to apply for the medic program.
If you have the time, I'd suggest:
- Anatomy & Physiology (1 & 2 if offered)
- EMS Communications
- Pathophysiology
- Medical Terminology
- Psychology (Intro. course)
- Sociology (Intro. courses)
The only thing I can think about, for a "pre-medic" program would be a BLS-review class... around here, every course does a week or two of BLS Review at the start of class.