Have you setup gimp print, as the 5n doesn't have postscript by default, and you'll need the correct drivers.
If you continue with problems, let me know, I have a 5n set up the way you have until the jetdirect card died. I currently have it set up through the print server of my router, but I'm looking for a cheap network card on ebay at the moment.
I'm just off to work, but will look at my queue more closely later if you need.
Cheers,
J.