Very good advice has been given to you I see (especially Storm), but there are a few fundamental things you should know about life in general, and about asking a girl out:
1) Girls are PEOPLE, just like you. There is no reason why you should sit here and wonder what you should say to this girl, because, more often than not, they're human just like you (there are some psychowhores out there that may be from another planet, but those don't count). So when you are interested in a girl, as someone said, the most effective way is to be direct in talking to her, just as if you were trying to make a new friend, but further.
2) Remember, you can only gain something. Either a friend, or a girlfriend. Right now, you're alone. If she says no, you'll stay alone, and if she says yes, you'll gain something, so why over think something that can only work in your favor?
3) Be realistic, yet optimistic about things. Don't over-analyze something that could have easily gone your way. Don't give too much value to something that isn't yours in the first place.
4) With all due respect, AIM is NOT the right outlet to talk to this girl, if you want something to come out of it. Talk to her in person. Prove your worth with her as she sees you. All AIM proves is that you need that barrier between the two of you to protect you from this monster that is her.
5) Use the one-two step "program." Every time you go one step forward, go two steps back. Show that you like her, but show her that you won't die if she doesn't return the sentiment. When you do something nice for her, don't cling. Just do the deed, and move on with your life. Make her realize how worthy you are, while showing her how worthy she is.
6) As has been told before, don't stare. When you talk to her, give her enough attention for the conversation at hand, and when that's over, that's over. This goes back to the whole "don't give too much value to something that isn't yours in the first place."
7) Lastly, have fun. If nothing, it'll be a good learning experience. Here's something I'd like for you to do if you want: Stand in some corner, whatever corner you choose to, and say hi, just hi, to at least 10 girls every day for a week. Tell me how you feel about talking to girls after that.
Originally Posted by Fat Syberia
I tried going out with a girl "just because" once; it didn't work. At all.
I did too, it sucked. It really never works. My worst break-up came out of a relationship like that.