Shoutbox

Set a static IP for your xbox and a different static IP for you pc. Connect pc to router wirelessly as you would normally, then go into Network and Sharing centre and select your PCs wireless and the ethernet port you xbox is connected to, right click > bridge. Make sure correct ports are forwarded to xbox aswell.

For detailed how to: Portward.com - Static IP on Xbox360

Portforward - Static IP address on PC

Forward 360 ports - Find your router, and select Xbox 360 on next page