How to talk to girl I like?

Just say "Hey xxxx, I don't know if you remember me but I was in your xxxxx class...and I didn't get a chance to talk to you so I wanted to at least message you ..."


or something along those lines.

I'd start casual.
Think of some common ground. Like you said - you had class together, but didn't really talk to her. If she too has myspace leave her a comment - something along the lines. "He, I didn't realize you had myspace, aren't you glad class is over? I don't think I could stand another day ..." And then talk about the class; give her something to reply to.
Something which shows you are easy to talk to. Don't just leave her a "Hey, how are you?" She probably gets a million of those, and the conversation will have little place else to go.

1. Hey I didn't know you had myspace. '' if she has it to ''
Or you can op for the casual lines?
Hey how are you.
2. I'm glad class is over.
3. Hang out with some friends, and offer her to join, and bring a few of hers along. You are being subtle, at the same time as all hanging out, you are getting to know her, take it from there...