Have a spare router lying around? Turn it into a wireless repeater! All you need is free DD-WRT firmware (get the latest candidate here), the instructions below, and you’re basically ready to go!
This How-To provides step-by-step instructions for creating a Universal Wireless Repeater appliance: a device that you can place anywhere and it will wirelessly repeat the strongest signal, onto another wireless network (with or without security). This functionality is also known as Wireless Client Bridge, or Range Expander. Unlike WDS, once you have this appliance setup, it will work with any open network.
Architecturally the repeater connects to another wireless router as a client, getting a single IP address via DHCP. Effectively the SSID network it connects to becomes your ISP. Therefore you (the client) will operate in your own IP address space, which is different from address space the repeater connects to.
How to Make a:
Universal Wireless Repeater