Problem - Plusnet accessing Xbox Live. Help

[#1]

Recently bought Plusnet broadband with a D-link single port wireless router and and after a long time changing settings and swearing cannot access Xbox Live. When I troubleshoot the connection on the Xbox it fails under the title IP address.
Any help and advice would be appreciated.
Cheers.

[#2]

How are you connecting the XBOX to the router?
Do you have your XBOX in the DMZ or have set up port forwarding?

[#3]

Ethernet cable and I havent a clue about the other question you asked, sorry, bad at this. cheers 4 answering tho any ideas?

[#4]

Might be worth providing some more info:
What model Router is it?
How is your box connected to the router via wireless or using an ethernet cable. If wireless, are you using the official xbox wireless adapter? 
Where is the router plugged into  (i.e. stright to the adsl filter, or via another router for example).
Typical basic setup is:
ADSL Filter into phone socket >> Router into Filter >> Xbox/PC into router
If it's connected to the router fine, but failing at the IP test, maybe your router does not support or have DHCP (needed in order to give the xbox an ip address).  If this is the case you would need to know what IP adress to give the xbox and set it manuall in the xbox config pages.