I was having difficulty with the same problem connecting my girlfriends brothers xbox to my laptop. They have a knock-off router that supports 3G cricket. They have Cricket because they live where no cable company want to touch. Anyways, they dont have the house wired up and the xbox is no where near the router, so I connected my laptop to the router and connected a cable to the xbox360.
(p.s. I dont plan on playing games cause its so slow, just do updates and download games and my gamer score.)
Now, Ive been following everybodys steps and I finally got it to work.
1. I did what most people recommended not to do on Win7, bridge the connection. Took me forever how to do this, but I got it and did it.
2. I read what other forum questioners across the internet, and I found that what you may need is a Cross-over cable, not just any network cable.
3. Making sure the Xbox is off when bridging the connection worked too.
It works really well, just really slow for how complicated of a process I am making this go through. I am pretty sure bridging the connection and using a cross over cable make a difference. So far I am testing it and able to connect to Xbox Live, woot. Now to make sure there are no problems.