I'm using a 7800DXL with much success.
The default ip of my router is 192.168.1.254. I used to have the 7800N, but it's been a while. I think it was the same ip, but can't swear to it, so definitely worth trying 192.168.1.1.
I think both routers are fairly similar in setup, but take the below and modify it if needs be. Like I say, it's been a while since I used the N.
ensure your PC/network isn't connected to the EWAN port.
A reboot of your PC may also be needed, just incase it's not recognising the fact that you're connected to a 'new' network. Had some probs with my PC in this regard.
If you're not able to connect via either of the above ip's, a factory reset of the router may be required. Just use a paperclip in the reset hole in the back, holding it down for at least 5 seconds.
Once you've got into the router, you can either run the quick start or go to:
Configuration -> WAN
add a new connection:
The WAN port needs to be set to Ethernet,
Type set as PPPoE
Description can be anything - 'Plusnet' for example
Enter your username and password
service name can be left blank
Authentication to AUTO
enable / disable the other settings as desired, but they can be left at their defaults.
You should end up with something that looks like the attached image, which obviously will vary depending on the settings you've enabled/disabled.
You can then go back into this newly created connection (click 'edit') and set any specific DNS or static IP address' if needed/desired.
That's about it really.
