I do mine the cheapest way possible. PC is right next to 360, use the wireless connection from downstairs and bridge the connection (with a $10 ethernet cable) so my 360 can use it too. Of course, I can only play Live (get it?

) when the PC is on, but it's always on anyway.
You can do the same thing if you have a laptop. Put the laptop near your 360, plug the ethernet cable into both, and use the wireless internet on your laptop to allow your 360 access to it.