I followed the cups printing howto the other day, and there was a rather important step mising. after using foomatic to make the .ppd for the printer, it needs to be copied to the /usr/share/cups/models (?? IIRC this is correct) directory. This really needs to be added onto the print guide.
I looked into it and this step is not necessary. Foomatic automatically adds a new printer to cups and copies the ppd file to /et/cups/ppd.