1.Have you made any recent changes on the computer?
2.Are you able to install other programs on the computer?
There is a possibility that some third party programs installed on the computer is conflicting with program installation process.
I would suggest that you place the computer in clean boot state and check.
To help troubleshoot error messages and other issues, you can start Windows Vista by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
Refer the below link to know more about clean boot procedure.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7