Of course it's a bad idea. But we're in high school, so it's okay! This will be your last high school party, meaning your last time to make stupid high school decisions. I say you go for it.
Best way to make sure people don't drink and drive is tell everyone they have to have a DD. At this party I went to a couple weeks ago, all the DDs had to wear these elaborate necklaces so that people knew not to let them drink. That's an idea? Oh and I'd suggest making your party BYOB, so that if people want to drink, and consequently drive, at least you weren't the one feeding them brewskies!