Answer
I had the same problem and heres what i did and it works for me using windows xp so it might be different if you have
another platform.
on the start menu click on my network places. once on this screen, under network tasks click on view network connections. double click whatever connection you use for the internet, and then click the properties button. select the advanced tab and under internet connection sharing select "allow other network users to connect through this computers internet connection." once done with that plug the ethernet cable from your laptop to your 360 and it should work.
