Just ask the department people how to get involved in research. The secretaries will know who you need to talk to, then go from there. You'll be the 10,000,000th medical student to ask about research and there will be 10,000,000,000 more until the end of time. They'll point you to the right direction. Just ask around, "Hey, I'm interested in some research in [insert field here]. Do you have any openings or know anyone who can help me?"
Pretty soon, you'll have to fend off the onslaught of offers.
Good luck!
-Todd MSIV USC