2 macbooks arguing

I have two macbook that can't browse the net at the same time one wins. They are wireless through an airportextreame. The airport extreame is connected though the wan port/modem port to a wired modem+router to one of the wired lan ports.

I think it might be somthing to do with that the port used in the wiredrouter is not a wan port, or its somthing to do with nat or dhcp any advice would be great?

Your Airport Extreme needs to be setup as an access point. Your cable router should be the DHCP Server. I would manually assign an address to the Airport extreme and have your cable router assign addresses outside that range. Your two MacBooks need to be setup to use the your cable router as the DHCP server.

Example:
Cable router 192.168.0.1
Airport Extreme 192.168.0.2
Setup DHCP server to assign addresses 192.168.0.3 and up.