I like this girl but I am too shy to tell her Help!?

Well, Im in year 11 and there is this girl i like, you can read about it in my earlier question. She is cute - nerdy. (simple way of describing her) the only problem is that I have a confidence issue. This issue occurs when in a serious situation (eg talking to all my friends in recess, very outgoing etc. Next period, presentation in front of the same friends and a teacher, face turns read, hands shake and all) and when talking to girls. Especially her. Im not too sure, Im willing to tell her I like her but i don't want to mess it up like I did with the last person and that was telling her on msn. (the only reason i did that was cause i couldn't tell her in person) so im just wondering, is there a way to cure this nervous breakdown i have? thanks in advance.