i had this same problem with the girl i like we are kinda friends not like friend friends we dont hang out but durning classes we talk abit and stuff and on msn we talk heaps.
she knew that i had feelings for her and all and this week i asked her out she said no and now her friends are trying to get her to go out with me.
i explained to her on msn that i cant stop thinking about her and stuff like that and that i hope our friendship wont be weird she said its cool i dont mind that you like me.

so just go ask her out you will feel crap for like 2-3 days after it(i still feel crap after 4 days but i really liked this girl) just do it if she is a friend asking her out shouldnt destory your friendship good luck mate =]