Mac Partition Disappeared! MacBook Pro Snow Leopard

This morning I was my Mac to listen to music via iTunes when it locked up. After a few attempts to force quit, it started again, then stopped again. A little confused, I attempted to force quit one more time to no avail. I decided to do a hard shut down. However, when I restarted the comp, it loaded the Windows 7 partition icon but no Mac OS X. I opened the Windows partition and I sat staring at a black screen for 5 minutes. I turned it off, let it sit for a bit, then tried to boot it up again. This time, it was ungodly slow in loading the partitions. Again, only the Windows partition shows. How could this happen? Should I just throw in the towel and start over with the install discs?

Reboot the machine and hold down the option key as soon as you hear the chime. (bong) Does the MacIntosh HD partition show up? If it doesn't try resetting the PRAM.

Let us know. If neither solution above fixes it, you may be looking at a reinstall of Snow Leopard.

Previously, well holding the option key the mac partition never showed and the windows did. I reset the PRAM and ended up with it very slowly opening my windows partition (my default). However, Windows doesn't ever start. It stops at the black screen just before the Windows logo would normally open. I've tried starting in safe mode, but it never gets past the black screen. I'm pretty sure I'm going to have to reinstall. Thanks for the help though.

Before you decide to reinstall, run a disk verify and repair on the hard drive. It almost sounds like the hard drive may be giving you problems so be sure to run a check on it first.

I attempted to verify the disk in which it said

Invalid B-tree node size
The volume could not be verified completely.

So I clicked to repair the disk. It told me that the volume was repaired, but then said it couldn't and asked me to back up what i could and then reformat the disk. Is it possible to do this same check with my windows partition? Or will I need to start everything from scratch?

No, it's not possible to just check the Windows partition. It sure sounds like your hard drive needs to be replaced. I wouldn't try to repair it any further or attempt to reinstall until you get a new hard drive.