Wireless bridging/repeater for neighbor's network

My brother lives in a rural part of Iowa. His neighbor, which is about 600 feet away, has some sort of internet through a standard Linksys router setup, with no wireless encryption. When I was visiting last year, I wasn't quite able to get on their network from my brother's house, but was able to drive just a few hundred feet closer to get my email and keep in contact with the world.

My brother has talked to his neighbor about using their wifi, and they have no problem with it. They are non-technical, so I don't expect to ask them to make configuration changes to their linksys.

So my plan is to purchase a pre-made wireless antenna and a repeater/bridge. However, from the instructions I'm reading, both devices have to have WDS mode enabled. Is there any other way of doing some kind of repeater setup without having to reconfigure the neighbor's Linksys? My brother's desktop system has a wifi PCI card installed on the ground floor, and I was going to hook up the antenna and repeater upstairs by a window so I can get line-of-sight.