Dont know about the DG834GT, but I am running on a bog-standard DG834, and have no probs whatsoever getting my server online...
Just make sure that:
a) You have a port configured in your lfs.cfg file that matches the port you have opened in your firewall.
b) If running on a SHARED connection, then you have forwarded the port to the correct computer on the network.
Honestly, setting up a router isn't rocket science, the DG's admin panel gives you more-or-less explicit instructions (right hand panel on mine
)
Also, if you are running windoze built-in firewall as well, then that is paranoia gone too far; disable the windoze one!!...the routers hard firewall is already as good as/better than anything coded by M$