You can play 4player multiplayer offline, so battling against your friends is indeed possible. however you can not play more than 1 online on one xbox i believe.
Some game support this with seperate gamertags on one xbox. However Call of duty seems to not.
You can connect 4 xboxs together and 4 tvs playing from the same house(broadband line) but thats about as close as you will get im afraid.