HP LJ 4000TN behind a firewall?

I have a LaserJet 4000TN hooked up to a network. I have it behind a
firewall. I'd like to be able to print to it from the outside world, so I
have port forwarding enabled and pointing to the LJ's IP address.

I've double checked the printer, I can print to its IP address from within
the network, so I'm assuming it's a port forwarding issue. I'm printing to
it from the outside from both PCs (XP) and Macs (OS X).

I have ports 631 and 9099 - 9103 set up to forward to the printer. Any ideas
of what I should do?

TIA,

Dave