Do you have Vista drivers for it? if not go to the Lexmark site and download them.
Unfortunatly I can't give you a direct link as I'm in Australia and I get redirected to the local site.
Vista drivers are listed.
Also you use the add printer option in Devices and Printers, not Hardware and Sound.
Make sure to follow the Lexmark instructions exactly for printer instalation, if you don't have the instalation guide, get it from Lexmark.