Taken at face value, you're having trouble with an Apple Application Support program file there. (Apple Application Support is where single copies of program files used by multiple different Apple programs are kept.)
Let's try something relatively simple first. Restart the PC. If you're using Vista or 7, now head into your Uninstall a program control panel, select "Apple Application Support" and then click "Repair". If you're using XP, head into your Add or Remove Programs control panel, select "Apple Application Support", click "Change" and then click "Repair".
If no joy after that, try the more rigorous uninstall/reinstall procedure from the following post. (If you've got XP, although the procedure is for Vista and 7, just read "Computer" as "My Computer", read "Uninstall a program control panel" as "Add or Remove programs control panel" and assume the system is 32-bit, and you'll be doing the right things.)
I did everything you said. I then installed itunes however during installation an errer message appeared. It reads "An error occurred during the installation of assembly 'policy.8.0.Microsoft.VC80.CRT.type="win32-policy".version="8.0.50727.6195".pub licKeyToken="1fc8b3b9a1e18e3b".processorArchitecture="x86"'.Please refer to Help and Support for more information. HRESULT: 0x..."