Since this suggests corrupted system files or a user tried to change all permissions on the startup volume, you will need to reinstall OS X:
Reinstall OS X without erasing the drive
1. Repair the Hard Drive and Permissions
Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.
If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.
2. Reinstall Snow Leopard
If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.
Download and install Mac OS X 10.6.8 Update Combo v1.1.
I'm not aware of that as a startup shortcut. To boot from an installer DVD:
Booting From An OS X Installer Disc
1. Insert OS X Installer Disc into the optical drive.
2. Restart the computer.
3. Immediately after the chime press and hold down the "C" key.
4. Release the key when the spinning gear below the dark gray Apple
5. Wait for installer to finish loading.
The drive is fine, but the permissions are still not. I have verified and 'repaired' a few times, but the permissions remain wrong, even though First Aid says it has repaired them. I have tried reinstalling and it has failed, saying it cannot load the support files. (This is from a bona fide Install disk.) Is there anything else I can do?
I can't really tell because the full directory name is hidden. But the message has to do with a directory's permissions, and usually they are indeed meaningless errors arising from past, updated versions of OS X.
Please provide more information on these crashes. In particular open Console in the Utilities folder and monitor it until one of these crashes occurs. See if the log entry helps point out the source of the crash. Also, using the Console's sidebar you can find the crash report based on date and time that can point out what crashed.
Don't post a crash report. They are very long and hardly any user knows what the mean.