DOE Recommended Process for Computers with an Evaluation copy of ArcGIS installed:

The work around is a protocol for this as follows - assuming that this error has NOT yet occurred due to system clock setback prior to moving from an evaluation to a full version of ArcGIS9.
If it has occurred, then a full system rebuild will be required starting with the manufacturer's original restore software or MS operating systems if build from scratch.
1. Backup any GIS non ESRI data or projects that you have stored in the C:\ESRI or C:\Program Files\ArcGIS or C:\Program Files\ESRI locations. I always recommend NOT storing new data in these locations anyway, but creation of a "gisdata" folder and "gisproject" folders outside of these program folders always to avoid just this issue if the program is ever uninstalled or reinstalled and overwritten. These two folders "gisdata" folder and "gisproject" folders should be on your data portion of your partioned hard drive to avoid data loss if a format is ever needed to be done of the program drive portion.
2. Before installing a permanent ArcGIS license on any machine which has had a working evaluation copy of ArcGIS9 installed, one must fully remove the ArcGIS9 evaluation copy using the proper WinXP control panel add/remove program process. Also to be safe, fully remove your ArcView 3.2 program if also installed.
3. Reboot the machine after the uninstalls.
OPTIONAL-Technicians only - Check the registry using regedit to ensure no ESRI or ArcView entries are present. In test units, both ArcGIS9 eval and ArcView 3.2 had been uninstalled, yet there did not appear to be any remaining registry entries on the test units after proper uninstall on units which had NOT experienced this error occurrence.
4. Install ArcGIS 9 full version and the permanent license. Reboot the machine.
5. Reinstall ArcView, as desired. Reboot the machine.
Future Technician Briefing Point:
If this error "The system clock has been set back to the past. This is not allowed". is reported by a user when attempting to run ArcGIS, then it is due to a system clock reset which DeepFreeze will correct or a manual reset of the system clock to the correct time again.
Prior to building an image, ensure that no evaluation copy of ArcGIS is installed. If so, then select a unit which has not had it installed just to be safe. Do the normal ArcGIS install and permanent license set up for the image. This should avoid this error situation from being more than a nuisance factor if students reset the clock.