A quick idea would be to examine your ip configuration for both networks.....you do not need a default gateway for your lan so if there is one remove it and set the ip static using something outside the scope of whatever your DHCP server is handing out. Then make sure your wireless connection has the proper default gateway pointing out to your routers inside address. Two default gateways will generally always cause some problems and since you are not going outside on the lan side just remove the default gateway. Let us know if this works