Problem Connecting Xbox 360 using Internet Sharing

Hi,

I'm having a problem with my Xbox 360 and how to connect it to Xbox Live.

My setup is as follows: There is only one available ethernet socket, so the Macbook has to be connected via that cable.

I'm then using the Macbook to broadcast an Internet Sharing wifi signal (sharing from ethernet to airport) as I am unable to use a wireless router in this instance. So far, I can connect my iPhone and Wii to the Macbook over this type of connection. But while the Xbox can detect the connection, the red light stays solid. So it won't connect.

I can, though create an ad hoc from the Xbox Dashboard - which the Macbook detects - and the wireless adapter light goes green - but the Xbox will then fail at IP Address.

Does anyone have any advice on how to proceed - as bridging the connection from the Macbook is my only option.