Also if it uses the Windows Installer there may be some scrambled data. On MS site somewhere there should be a Windows Installer Cleanup Tool for download. Maybe if you look at the uninstall string you can tell if it's Windows Installer based.
I remember when I first got Vista I'd run a program and it would ask me if I wanted to install it when it was already installed. The cleanup tool fixed it.
I don't know if W7 had the same issue.