Hm, interesting. You need to get a router with an 802.11whatever WAN-side with a wired network behind it, probably on the lowest budget possible... Scary thing is I've actually done this before. I think the easiest way to do this would be to create a bridge, to convert the wireless signal into an Ethernet signal, and then connect the Ethernet cable to your router.
One way that might work is to use a game adapter, such as the Linksys systems that are used to connect wired game consoles to wireless networks, except connecting the Ethernet cable to the WAN port of your router. This is the type of adapter that I am thinking of: http://www.amazon.com/Linksys-WGA11B-Wirel...r/dp/B0000AJVBW
. There are others, depending on the type of network.
If that doesn't work for any reason, you could always get an old WinXP computer, install a $10 PCI wireless card in it, and bridge the wireless and wired network connections, then install a software firewall. This would turn the computer into essentially a firewalled gateway for your network. You would only use this computer to handle authentication on the wireless network and to bridge the connections (it becomes your equivalent of a cable modem).