Which version of windows (or other o/s) are you running?
A google search using: xbox pc share internet provides many links that should help you setup and use windows internet connection sharing with your Xbox 360.
We need detailed information about ALL OF THE HARDWARE in your system.
We can best help you after you create a detailed hardware list in the System Specs portion of your
forum profile http://forums.tweaktown.com/profile.php?do=editprofile at the bottom of the
profile page or in your forum signature http://forums.tweaktown.com/profile....=editsignature.
Be sure to include brand names and model numbers.
Click on my PC Specs information to see the level of detail that you should provide.