How do you totally remove a program from WinXP Pro?

I used Norton's Clean Sweep to remove a program from my computer. I went to the file folder and removed the remaining files and folders, then I went to REGEDIT, and went to Hkey_Local_Machine\Software\Microsoft\Windows\Curr entVersion\Uninstall, and deleted the key for the program I wanted to uninstall. I have rebooted, gone to the control panel/add_delete programs, and it still shows in the list of programs, but it does not have an option to remove it. It just says, "Used ocassionally"

When I try to install a new version of the software that I am trying to delete, I get the message that a previous version of this software must be removed before I can install the new version. How do I remove this program from my computer completely?