Hey Matt,
Suggestion: If GaRHaR hasn't already given you the fix, you might try simulating the network in-house so the speak. Eliminate the phone lines and connect a computer directly to the router. If you can get it working that way, then you have narrowed down the problem.
Remember KISS. (Keep It Simple Stupid)
This may be old news, but something I found:
By default RDWC uses port 80. You will have to login to the DG834G and create an inbound rule for wan traffic over port 80 (or other if changed) pointing to the local IP of the computer running RDWC. Also on the computer running RDWC check the Windows firewall settings to make sure it is allowing it as an exception and if the port was changed then you must create an exception in Windows firewall for that port.
Also, are you using the same Windows O/S on both ends?
Good Luck...