If you really like this girl and want to have a relationship, then truth is probably the way to go. If you start dating her and she either finds out for herself or it gets to the point where she will feel lied to when you do tell her, it will be worse. If you tell her up front, you will save yourself and her a lot of grief if she doesn't accept it. If she does, then great. It may take her a bit to decide where she stands, but she already knows you as a guy, so its just a matter of whether or not she can deal.
sam1234