i just redid my bedroom into more of a living room. futon, counch, TV. my router is downstairs and i was told taht i could bridge the connection from the laptop to the xbox 360 through a crossovercable
what dont you want to spend money on? im not familiar with the 360, but why would you need to buy an "adapter" if it already has an ethernet hookup?
if your laptop has a wireless connection and an ethernet port, you SHOULD be able to connect to your internet wirelessly with the laptop, then send the connection out through ethernet to the 360.
i did that a while back, although not with a console. you basically use your laptop as a router.