have you tried the web-based config tool?
try going to
http://127.0.0.1:631 in your favourite web browser, and see if all of the correct drivers are listed there. If they are.... well.... you might just want to use that for now, as I'm not familiar with GNOME's printer setup. If they're not, you may want to consider installing the cupsomatic package (that's what I did on my debian box)