Evening, a quick search on the forum failed to resolve my issue so I am posting details here...

-----------------Setup-----------------

I have Snap Broadband connected to a THOMSON ST5x6v6 which is connected via ethernet to a DLink DIR-825 wireless router.

DIR-825 External IP: 192.168.1.64
Xbox 360 Static IP: 192.168.0.254

---------------Settings----------------

* I have UPnP enabled on both devices.
* Thomson: DMZ applied to 192.168.1.64
* DLink: DMZ applied to 192.168.0.254

Essentially I have made the DLink a DMZ on the Thomson and then made the 360 a DMZ on the DLink. This is following advice on www.portforwarding.com. Without DMZ's NAT was still strict (UPnP only)

However my NAT is still strict. Snap have told me they do not block anything so it's a local issue.

---------------------------------------

Does anyone have a clue on how to resolve this? It's driving me mental not being able to connect to some parties on XBL and a select # of people being unable to connect to me (though we can usually both connect to an intermediary)