I'd suggest that you don't try to access the admin services directly from outside: you'll spend time trying some exotic forwarding to get it right and it likely won't be very secure. For my purposes, I usually ssh into a machine inside the router's network and use lynx from there to connect back into the router's admin services. The character interface is a bit rustic, but it works for me. It probably won't work for admin services that want to do fancy-schmancy javascript-based whizzies.
(added later:) For a little fancier work, you can use ssh -X
to get Xwindow traffic forwarded to your desktop - this allows you to start your favorite graphical browser (e.g. Firefox) on the target machine to see the admin screens of the router.