You need to get your stuff backed up immediately. Don't do anything else until you back up. Use Disk Utility's Restore button, while booted up from the install disc, to make a complete copy of your internal drive to an external drive. Then you can try DiskWarrior or reformatting/reinstalling.
Stolen from MacWorld.
8. Back up a drive
Looking for a free way to back up a drive? Well, you’ve already got one—Disk Utility’s Restore tab. It’s a somewhat crude tool, but it does work. Launch Disk Utility and choose the Restore tab. Next, select the volume you want to back up in the left column, and drag it to the Source text field. Select the volume that will hold the copy, and drag it to the Destination text field.
If you want to erase the contents of the destination volume before storing your backup files there, select the Erase Destination option. Otherwise, the newly stored data is simply added to the existing files. Click on Restore to make a copy, and the backup process is complete. If you need to use your backup files later, simply reverse the Source and Destination directions.