reinstalled xp and now I can't uninstall a program...

My itunes for windows didn't work after the
reinstallation, so I tried to reinstall it but every time
I do I get "Error: -1605 This action is only valid for
products that are currently installed." The problem is I
can't uninstall the old version of itunes (doesn't work
from Add/Remove) and I've been told that this is a
Windows Installer issue. I downloaded Windows Installer
Cleanup, but when I run the program itunes doesn't show
up in the box. What do I do now? Please help!