Eircom Zytel + Port Forwarding for a slingbox

I dont see any previous threads on this 'new' Eircom modem and how to set it up to allow a slingbox to broadcast outside of the LAN, so I'm going to ask for help from anyone who knows how.

Eircom lumped us with this cheap as chips looking Zytel 660HW a while back after our old one broke. Im not in a position to buy a different one right now. The slingbox works itself, but im presuming port forwarding is blocked on the new modem. It may sound like I know what that means, but I haven't the foggiest.

Logging in to the Zytel admin page within a browser is fine, but I cannot get the supposedly 'easy' slingbox setup service to play nice with it: i.e. slingbox software prompts me to log in to zytel which constantly fails (it requires a username Im not aware of, despite knowing the password - no success with using default usernames).
So I tried manual setup within slingbox, but it doesn't behave as it says it will in the help video (instead of seeing a 2-frame browser window - one with the Zytel admin page and a second side frame with the correct slingbox settings to be copied in - I just get the Zytel admin page on its own...basically back to square one).

Ive tried changing this myself manually as admin, under NAT > Port Forwarding. But the suggestions on portward.com don't work because Zytel won't let me enter user-defined 5001 port forwarding with a server IP address of 0.0.0.0. - it gets stuck and says IP format error !

Does anyone have any experience with this? It's driving me nuts!

Thanks a million