is "connected to broadband through our local wireless network" - what does that mean? Is it your wireless network, or is it operated by someone else? Is the connection being distributed by a wireless router? If it is, the router may have its own DCHP server and be assigning IP addresses - or trying to.
You say you have assigned IP addresses, but that the broadband connection has its own fixed IP address - is this something that has been arranged with your ISP? ISP's are not keen to assign fixed IP addresses to home users for obvious reasons - the world would rapidly run out of available addresses.
Perhaps you'll provide some more detailed information, then one of us can be more helpful.