Cheers dude for the tip but i fond this somewhere and tried it and it works fine - if anyone else has this problem try this:
"I've done this before. My Xbox 360 is plugged into my PC, and my PC wirelessly connects to a wireless router.
You need an Ethernet CrossOver cable, not a patch cable. Plug the Xbox 360 into the NIC on your computer, right click My Network Places, click properties. Now right click your wireless NIC, go to properties, then go to Advanced. Click Allow other users to connect through this computers internet connection, and select the NIC the Xbox 360 is using. Click OK. Now right click the NIC your 360 is using. Click properties, then scroll down to Internet Protocol. Click Properties. Click Use The Following IP Address. Make sure it says IP Address: 192.168.0.1. Your Subnet Mask is most likely 255.255.255.0. click OK, and close out of that. Check the IP you are getting from the router. Write that down. Go into your Xbox 360 Network Settings. Change the IP to manual. For the IP, enter something like 192.168.0.x (x can be any number from 1 to 9, make sure your router hasnt assigned this IP to another computer). Subnet Mask should be 255.255.255.0, DNS1 should be 192.168.0.1, and DNS2 should be 192.168.0.x (x can be any number from 1 to 9). Tell me if it works. There may be other setting you need to enable on your setup."