Should I tell her how I feel eventhough she has a Boyfriend?

Unless she feels strongly for you, she will most probably tell you no, she has a bf, even if she wants you. It's because she has to be loyal to her bf. it's a question of honor.
You can also read her body language and signs, and try to make a move on her.
Just my humble opinion.

WOW I was the girl in a situation exactly the same as that.chances are she knows how you feel already.us girls are pretty good at that.but I got to know the guy really well as a friend first and he came to realize that my boyfriend was abusive to me and I had been too afraid to tell anyone but he helped me soo much and was just there for me and eventually he helped me get the strength to break up with the loser.so now we have been dating for a few months and he is being deployed to iraq in 10 days :( he will be gone for 15 months so I don't know what I'm gunna do without him

wait! don't get yourself in a drama fest. Just keep in touch with her and see what happens but whatever you do DONT get in the "friend" status with her! good luck

Yea don't tell her anything like that. That's going to be really awkward after and not a good thing if you want her if her other guy falls from view. Its probably worth the wait!