Girl's opinion:Read whole thing please!Let her know that you like her. Don't know how? send her a note saying "I wish you were going out with me" or "I really like you, and I was wondering if you liked me too, more than your current boyfriend", and if she's snobby, then she'll probably go to the one with better looks. But you either need to get through that part of her, or find someone less self centered. If she's nice, she may put you off 'in the nicest way she can' or agree, as long as you have a good attitude about it!
Boy's OpinionIf her crushing on the guy is more because of the looks, then unless you get some plastic surgery or cosmetics procedures done, I don't feel she'll look your way. But if you know that she likes the particular guy for his behaviour, attitude, his character, then the easiest way to get her attention is to be better at it than him. Alternatively, if you want to win her over, you should make yourself more visible to her, and help her out whenever she needs it, or stand up for her when no one else is, and show her (whether discreetly or openly is up to you) that you're the better guy in mannerisms and gentleness. Trust me, girls appreciate it and develop a soft spot for guys and people in general who help them when everyone else is looking the other way. Just make sure when you're helping her that it doesn't come across like you want a chance with her.
An Adult's OpinionYou can't MAKE someone feel the way you'd like them to feel. The little games and machinations may succeed in the short term; but a girl who'd fall for them would be gone as quickly as the next little game was played, leaving you with a battered ego or worse. Fantasize about the girl as much as you like, but look for someone that will make you feel good about yourself in the long run.