Wirelessly bridging wireless networks with Wireless Distribution System (wirelessly): WDS is a very simple idea: it allows an access point to act like a port on an Ethernet switch. With this simple idea, Apple, Linksys, Buffalo, and others have finally implemented inexpensive and simple-to-configure bridges. What's better, Apple and Buffalo, to name two, allow their access points to work as APs and bridges simultaneously, which can let you create a cloud of access instead of a little pool. It also reduces costs.
In a shocking discovery, which I write about in this article, you can use Buffalo and Apple equipment together in WDS mode. Buffalo's roughly $100 access point (WLA-G54) pairs with Apple's $200-$250 AirPort Extreme Base Station, which has all the gateway features you need. There's even a Windows configuration utility available for it (in beta testing).