to be honest, if you don't want to creeep her out, you HAVE TO MEET HER FIRST in a friendly manner, and then slowly flirt with her when you become familiar to her, to show that you are interested...when strangers flirt with women, they get freaked out and you're seen as a creepster...say hi and introduce yourself, or even better, find some excuse to meet her so you can be friends first
Whenever you see her, catch her eye and hold her glance for like 2 seconds,smile, then next time you see her smile and say hey. facebook/myspace message her (since you don't have her number) a day or two later, start friendly talk, do not say that she is beautiful or hott or anything like that. Just have a lot to talk about. When you see her again it will be easier to go up and talk to her. Once you talk to her, if she seems interested, ask for her number and go on from there..