Try looking for computer software -I have a CDROM (it's old) called "Guia medica para la familia" and it has search features (based on symptoms, illness, med) and descriptions of illnesses, medications (think a mini web-md).
Also, a lot of the state health depts do their information sheets (on the web) in both English and Spanish, so you can print topics as necessary -I like NY.
If you're in a state w/ a lot of hispanics, or near the border, you might find some useful books in the bookstore. If in MX or other Spanish speaking countries, shop a bookstore near a university, they'll have handy charts for their students and they're affordable.
Lippencotts has a medical eng/span dictionary w/ added stuff like anatomy charts, common phrases.
If you don't speak ANY Spanish: take a course over the summer that will help you with pronunciation, or go to your school's Spanish dept and see if they have free conversation tables, or similar get-togethers, to work on your accent. Knowing the vocab is useless if you can't speak. And don't worry about listening comprehension if you're just starting, when someone is worried/sick/drunk you're gonna have a hard time understanding them, you'll have to go to a "si/no" and pointing-type question format. Want to improve listening skills? Go work somewhere with a lot of hispanohablantes over the summer (not vacation or school, work).