Is your Xbox 360 in a room far, far away from your broadband router, and you just don't have the cash to spend on the Xbox wireless adapter? You can get online easily by hijacking your laptop's wireless connection with the following tools:
And the steps to get it all connected (note, I am using Vista Business here, but the same or similar steps apply for other operating systems):
Note! If you need to download an update for Xbox Live, do it through the Xbox Live tab rather than the System Test tab, I had better luck there.
Big thanks to my friend Henry Hernandez who suggested this originally, he's the kind of smartypants who makes his own crossover cables.