I was in the same situation. I liked a girl Freshman year in High School and she liked me back. I'm certain she did, it was that stare, from accross the room that would go away once you looked back at her. Yet... I did nothing. Basically, all I did was say "hi" to her. I was way to afriad to make a move. Unfortunetly, I don't have a happy ending. As time went on, all the way to Senior year (yes, a 4 year crush) I began talking to her (we had, in fact HAVE 2 classes together). She seemed to be flirting for a bit, and we talked pretty often. Maybe I'm really bad with the signs, but I was certain she liked me. So... I told her I liked her... since Freshman year. Apparently, she didn't like this. I don't know what I did wrong. She suddenly stopped talking to me. Ignoring me. Two of my friends (both girls) said they thought it was adorable that I had a crush on her that long. She didn't think so. I have yet to speak to her with the exception of papers being passed in class. She wasn't worth.
I'd hate to scare you but just be careful. At least now that it couldn't have blossomed into a good relationship. If I hadn't told her, I would've gone on wondering. Even with the bad parts, its worth it just to go for it.