Hey cdw--
I'm going to assume that you're a guy. That would fit the profile more--"I can't dance but my date loves it." If the girl can't dance and her date loves it, no problem. She should get on the floor and let the guy do whatever he wants. Well, maybe not whatever--but within the protocols of dancing.
If, on the other hand, you are a guy as I believe you are--listen to Miss Kitty. Take lessons. Privates can be expensive, but there are a lot of places that offer introductory packages for considerably cheaper. The only thing is, if you're like 17, they may not be willing to sell or pitch to you. The chain studios especially are in the business of making lots of money, and they sometimes establish age minimums. However, if you just go in and honestly tell them what you're looking for, they may be able to set you up with something.
Independent studios will definitely be able to work with you--and you may find some soft-hearted instructor or other who's willing to come down on her normal hourly fee to help a teenager in love.
Another thing you can do is attend a number of group classes at a local studio or club. Learn some basics in several dances that you think may be appropriate for your prom and then set up a private lesson or two to help fine tune what you've learned. That may be the best and cheapest way to go. Again, if you find a teacher you can work with and tell her what your situation is, she may be able to give you much more specific advice about where to take lessons and in what.
One thing's for certain--you won't learn to dance by hanging out in front of a computer. All of us on these boards take lessons, even those who teach dance, group and private.
BTW, if it is hip hop you're looking for, there are lots of places that do hip hop these days. We even have them in Nashville--so I know that you can find them!
Cheers,
Genesius