Wierd. Maybe your antivirus is interfering? Try disabling it and any anti spyware type programs. If that fails try to install in safe mode. You have to add a registry entry and run a command to do this...

http://www.winvistaclub.com/e40.html

or

http://www.windowsitpro.com/article/tips/jsi-tip-9233-safemsi-exe-freeware-starts-windows-installer-...