Is the only reason you like her because she is 'hot'? Well, if that's the case, then I wouldn't want to go out with her at all. Just because someone is hot doesn't say anything about their personality or character. It just shows the way they look physically, which only matters a little in a good relationship. If she's a jerk, don't even THINK about asking her out, because even if she says yes to you, she may just start flirting with your best friend next week. :S
If she is nice and 'hot', then here's what to do:
Get to know her a little better, talk to her more, sit next to her when possible, and make eye contact. When you've become her friend, then just see how things go. Hopefully, the outcome will be positive.
Good luck,
CB