Check that the Date in the machine is correct.
See if there are Access Permission problems with these Registry Keys also.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
minor bug integrating IE7?, nlite 1.2.1
http://www.msfn.org/board/minor-bug-integrating-ie7-t86346.html
Have you also tried right-clicking on a Uninstall.exe, or Setup.exe, and choosing the "Run As Administrator" option?
If you type %temp% in the Start RUN box you could clean out all the temp files (that are able to be deleted), Programs dump a lot of files in there with each failed attempt.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/default.aspx/kb/929135
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista
http://support.microsoft.com/kb/936212/#appliesto
How do I restore security settings to the default settings?
http://support.microsoft.com/default.aspx/kb/313222#appliesto