As a follow up to last week's post on the Windows Installer 5 and Windows 7 problem; I have come across a solution for the more tech savy in one of the forums that I would like to pass along.
The solution involves going into the registry, not something that the every day user should take on, and if you don't feel comfortable performing the procedure yourself, consult your IT expert.
The procedure involves copying the correct registry key from a healthy machine to the sick one. If your machine is still healthy (i.e. still able to load and delete programs via the Windows Installer) you can back up the key to a file in case your key gets corrupted.
The directions for the fix can be found here.
Before doing any work on the registry remember to back the whole thing up. Your IT expert will be glad to assist.