xbox live and wireless lap top using same ip address?

[ex33764]

i dont know if anybody else has encountered this problem but im using a wireless internet adapter for my xbox 360 and my brother has a laptop and im guessing were both using the same ip address becuase every time he is on the internet it will not let me in to xbox live or vise versa. Is there any way i can be on xbox live an my brother can use his laptop without one of us being disconnect from the interenet? im using a Linksys WRT54G wireless router so if anybody can help me out on this situation i would greatly appriciate it thx