Photo Booth is located in your Applications folder, look for it manually.
It's updated along with Software Update and with 10.6.8 it's at version 3.0.3.
If your searching for it wrong, it's two words Photo Booth, not Photo Booth.
If it's still gone, it can be reinstalled, however Photo Booth is one of those programs that can only can be reinstalled via 10.6 machine specific disks with a reinstall of OS X. It's not in the bundled app installer that does iLife.
Luckily this doesn't involve wiping your present third party programs or files, (should backup regardless) just writes only OS X and bundled Apple programs from the older disk copy, then Software Updating fully to bring all programs up to date.
Your going to need the 10.6 machine specific disks that came with your computer, hold the c key or option key down to boot from the disk, then simply reinstall OS X.
Quit and reboot, then use Software Update to get current.
Some third party programs that install at boot kernel extension files into OS X will have to be reinstalled from original sources. You'll know as they won't work anymore.