I live in a property that has two houses -- one main house (basically a cottage), and one guest house that I use as an office. My wife has a small office in the main house, and for years now, she's had to put up with the wireless internet connection there. I've been using a Linksys wireless-B router (B because of its greater range), and she has had a variety of older Macs in her office. Right now she has an older iBook that does not have a wireless card installed. I've had her using a D-Link wireless Ethernet bridge for two years now, but that died. The main house and the guest house are about 100 feet apart.
I had squirreled away Walter Mossberg's excellent article from the Wall Street Journal that recommends the newish Powerline adapters to get an Internet signal around homes. He recommends Netgear XE104 Powerline adapters. I bought a couple of these from one of my favorite computer-supply online suppliers (newegg.com) and sure enough, these Netgear Powerline adapters solved the problem. My wife now has a fast, reliable Internet connection as opposed to the stunningly slow wireless connection that we used to have. This was a stunningly easy way to set up another Internet connection in a separate room. The only problem I had was that these were fairly expensive, at $60 per unit -- and you need at least two units.
A few weeks later, I noticed that Fry's in the Bay Area had some Airlink Powerline adapters for sale for $25 each. I bought two and installed them in my parents' house. My mother now has a consistent and reliable Internet connection, too. The Airlink Powerline adapters were just as easy to install as the Netgear ones, and they cost less than half the price!