You can do this via some editing in the Registry - if you're not comfortable with using and editing the registry, make sure you back it up first.
Click on Start, type in regedit and press Enter. Go to the following key:
HKEY_CURRENT_USER – Printers – Connections
Click on the printer you need to remove, and either right click and click 'delete' or just press the delete button.
You then also need to go to:
HKEY_LOCAL_MACHINE - SYSTEM – CurrentControlSet – Control – Print – Providers – LanMan Print Services – Servers – Printers
Under the printers key, expand it and you should see the name of the print server that hosts the network printer. Expand that and you can then delete the printer from the list.
You'll then need to close the registry editor and reboot your computer.