I agree with the just asking her out on a simple date. Maybe it's just me but I'd freak out if a guy came out all strong with, "I like you, will you go out with me?" Just NO, I'd be flattered but if I didn't know the guy too well I'd be scared...
So just ask her out. Take it slow. Enjoy her company. If you like this girl so much, take the time to get to know her. =o Who knows? You might find out she's a complete she-devil and your crush will dissolve into nothing. Or she could be an angel and you two may become an item. You never know until you try.
Oh I should warn you, don't try to be her friend. I mean be nice to her sure, but once you fall into the 'best friend' category it's hard to get out. Asking her out on a date is a nice subtle way of telling her, "Hi! I'd like to get to know you better!"
Good luck. ^^ Hope it works out for you.