in the set-up of the xbox you can (instead of using auto)assign an ip as long as its in the range of 192.168.1.0/100.
you then need to assign each pc/laptop its own ip(also within the 1/100 range).
put the ip assigned to the xbox outside the nat.
don't auto assign ips on the laptop/pc's. as this will just create a ip conflict and you will lose your connection.
