xbox live modem problem

my 360 isnt by my computer

but can i still buy a modem and then use the ethernet to connect to the back of the modem im getting???

get on to xbox live duh

how? my 360 is clear across my house and the apadter wont work because my wireless router is too far away

but can i just buy a $80 modem and hook it up to the back of my xbox 360 without it by my computer