Hmmm. This same thing happened to me after a coworker ran an old copy of Norton Utilities on a G4 under OS9, then tried to boot back into OS X.
Do this. Get out your gray set of disks that came with the computer. Do whatever it takes to open up the cd/dvd drive up, and put in the system install disk. (No gray disks? Do you have a copy of Panther or Tiger in a box? They will do too.) Push it in, reboot the computer, and hold down the c key to make the Mac look at that disk.
What you are trying to do is re-install OS X without reformatting the drive or losing any of your data. Whatever caused your initial problem that made you need DiskWarrior, that problem hosed important stuff in your system that DiskWarrior can't fix because it is Apple's.
When the disk finally boots up (you can let go of the c key after you see it starting to boot), the installer should appear. Read the instructions and look for the button that lets you configure your installation. You are looking for "Archive and Install", or something close to that. Choose that option. That option will pick up your preferences, user settings, and all the stuff that applications install into the system, so that you don't have to start from the beginning like you would if you did a clean install. It will, however, completely replace all the Apple-made parts of your operation system with fresh, unbroken parts.
After the installation is finished, reboot off the hard drive, and immediately go to Software Update under the Apple menu. Run it, and be patient, as you may have to download, install, and reboot your Mac a few times to get everything updated to the latest stuff.
Hope this helps.