I have just bought a wireless router so i can stream videos to my xbox in the living room and am needing some help setting it all up.

I have a wired belkin router for a couple of years and had no problem with it but i am in the attic. My house mate has a cable running from my room down to his on the first floor for his laptop.

my plan was to put the wireless router in my house mates room using the cable thats already there to connect it to the router in my room. My router lets you do this by putting the cable into the 4th port and pressing a switch. The wireless router could then be used to transmit to his wifi lappy and my xbox downstairs.

im ill so dont have the energy to set it all up and try it out tonight but i can do what im planning cant i?

If your router allows one of the ports to be inbound then yes, you can do this. However, it would be a bit unusual and some of the settings could get confusing. You may find it simpler just to switch out the existing wired router, if the wireless signal is strong enough.