You need a bridge.
A bridge is a device that connects two networks like they are one nework even if they cross mediums. The easiest solution would be to get wireless bridges like those used for game consoles. These bridges will talk and work right out of the box since they were made for kids.
You're only going to get a couple hundred feet range if you're lucky with stock antenna. You may need to upgrade.
A bridge can cost $50+ High-end Low-end
A high gain antenna
(Outdoor, directional) $100+ without cables, connectors or mounting hardware.
....and, yes, you can get bridges that support WEP and WPA, but they'll cost more and require some config.
You can read an overview of wireless/wired network bridging here