You could also try System Restore to get back to before you downloaded that file.
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista (or 7)
http://support.microsoft.com/kb/936212/#appliesto
How to analyze the log file entries that the Microsoft Windows Resource Checker (SFC.exe) program generates in Windows Vista
http://support.microsoft.com/kb/928228#appliesto
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
When installing any software have you tried right-clicking on the shortcut to the program, or the .exe, or Setup.exe, and selecting the "Run As Administrator" option? Do so even if your user is an Admin.
See if there are any clues in these for your webcam problem. Is it even listed in the Device Manager?
If you are having two different problems then splitting them over two posts might be a better way to go unless you think they are related problems.