Some trouble getting girlfriend. I think I like someone but I'm not sure if she likes me back? Ways to ask out

There is this girl I've known for more than a year who I think is supercool, not the best looking girl on the universe but just fine and intellegent that really like but she was going out with someone else, I thought about asking her out but then she kinda dropped in the conversation she was going out with this dude. I though I missed my chance but they recently broke up but I think she might still like him.How long do I have to wait to ask her out? I feel we connect when we are on msn every once in a while but I'm not sure how to know if she likes me becasue I act really stupid not likein a goofy cool way but just sound really really extremely big headed or like a complete retard but I'm ussually a nice guy (I think) who is a bit shy but I know if someone challenged me to ask any girl in a party fro somoene else I'd probably do it, but only if they challenged me if I was to do it alone for me I peee my pants.Do you have any advice on what to do,should I wait more or ask her out & how?