ckent's numbers are right from all i've read, but these are mostly for "open-bore needles", like if you drew someone's blood, then stuck yourself with the needle. The risk for, say, a suture needle, is less. This is intuitive, b/c there is much less blood volume transmisible on a suture needle vs. an open-bore needle.
Your school should be vaccinating you for hep B. Some elementary schools are even beginning to require this vaccine for kids to attend in some states, so hopefully soon everyone will be vaccinated somehow.
I can't imagine that any of these would keep people from practicing medicine in non-bloody specialties. If I had one of these viruses, I think I would avoid a surgical field, as I would not want to chance putting my patients at risk should an accident happen. However, there would be very low risk of a psychiatrist giving a bloodborne virus to a patient. There are plenty of medical specialties that do not involve needles, so there would be no need to fear loosing medical privileges entirely.