Another vote for "you should consult a lawyer." I'm guessing you don't know whether the law varies from state to state, or even city to city, and so whether what you'd read (books, magazines, on the Internet...) would be valid where you operate. If you're going to do this as a business, it'll be money well spent.
That said, I've really enjoyed reading Katie Lane's blog on legal advice for freelance artists, including contract-related issues,
Work Made for Hire. She also offers legal services for freelance artists, but I can't vouch for it-- I just like reading good and interesting writing.