I posted a How to Remove Printers guide on the excellent Spiceworks Community some time ago, but the link to the Printer Deleter has already changed a few times.
In the event that the link breaks again, you can download the Printer Deleter here instead.
If that doesn’t work, the final option is to reset the print spooler to factory defaults. You can do this by running Reset Print Spooler – MicrosoftFixit50126. Here’s some info on using it:
This Fix it Solution automates resetting the Print Spooler on Windows XP, Windows Vista, Windows Server 2003 and Windows Server 2008.
The Fix it has two modes: Light and Full. The light mode will make changes to the spooler that should not require the end user to make any changes. The full mode will restore the print spooler to defaults and require a reinstall of printers.