I know that this is possible because I helped my friend do it a while back. I want my laptop to be connected wirelessly, than my 360 plugged in by Ethernet to my laptop and get online with it.
They sell Booster or expanders hubs. Pretty much a little box with a antena. Takes the signal from the host router and expands it allowing a stronger signal.
Alright cool, let me make sure I understand though, you just put it anywhere where the signal reaches(not directly plugged into the router) and than it amplifies it?