It's nothing to do with port forwarding, wifi or anything else. The DG834GT with official (Netgear) firmware doesn't have NAT loopback. If you flash to DGTeam firwmare not only will you have more security features at your disposal, you'll have telnet enabled by default (for LAN admin users) and also NAT loopback.
Flash to DGTeam fw, and you'll be able to loop back through the router to your own public IP WITHOUT seeing the router's login page

Easy once you know how. At the moment, you're trying to access your public IP but the router is recognising that you're doing so from inside the LAN, so it presents you with a login prompt. NAT loopback will effectively mirror your request on the internet and back in again as though you were connecting from outside the LAN. Sky User (forum) have details of how to flash the DG834GT safely (and retrieve your Sky username and password).