Same thing happened to me (I even started a thread about it here). If you're still under warranty/have AppleCare, Apple will most likely fix it. At least that's what they told me. I didn't have AppleCare and my warranty was expired, and they quoted me a repair price of around $300. The guy at the genius bar actually told me how to fix it myself, which I did. It is not an easy repair at all. Unless you're very confident with your ability to disassemble and reassemble electronics, I don't think I'd recommend it. However, if you feel you're up to it, go to ifixit.com and download their guide for replacing the optical drive (you don't have to actually replace the optical drive, you just have to take it out).
Whatever you do, DON'T try to disassemble your PB without an iFixit (or similar) step by step guide. You'll never get it back together right if you try to do it on your own. Use iFixit's screw guides to keep track of the many tiny screws that you'll have to remove and then put back in exactly the right place.