When I attempt a system restore, there is no calender shown. If I use the wizard to set a new restore point, the new one is shown in the list under a point made for today, however, when I go back and attempt to restore, the calendar is still missing.
I'm not sure if you have been able to correct this problem, after your comment of "above my skill level".
Assuming you have Windows XP, you can go to the following site and it will do the registry change for you.
This small GUI (Graphical User Interface) utility will check the Registry associations that cause this problem, and notify you if they need to be corrected. You will then have the opportunity to correct them, by clicking the Repair button. This application is freeware.