How do I build a point-to-point wireless connection to a neighbor's house?
Start off by making a couple of DIY cantennas. Then purchase a couple of wireless access points (WAPs). Consider the D-Link DAP-1522 Access Point or the Cisco-Linksys WAP54G Access Point. We use Linksys products however, we are not shills for everything Linksys. In fact, we dislike their use of outsourced tech support. Look at Dlink, Netgear, Belkin and ActionTec bestselling wireless access points (WAPs) and others and decide for yourself.
Set both of the APs to run in point-to-point mode. Configure the APs via a browser. For the WAP11, change the antenna selection setting to use right antenna only.
You'll need a couple of pigtails (N male to RPTNC male) to connect your access points to the cantennas. Shorter coaxial cables are better. If there needs to be any long cable runs, make it the ethernet (UV-resistant for outdoor environments) cable from the computer to the AP, not the coaxial cable from the access point to the cantenna. A Wi-Fi AP can be wired to a gateway with up to 328 feet/100 meters of ethernet cable.
Connect in this way: antenna >> pigtail >> access point >> ethernet cable >> computer
Protect the APs by putting it in some sort of weatherproof enclosure (radome) with a hole cut for the pigtail. Some people have used plastic food containers (Tupperware), but you may want to use something made out of aluminum or steel that was designed to enclose electrical and/or electronic equipment. Metal NEMA (National Electronics Manufacturers Association) rated electrical enclosures are typically found at stores like Home Depot. In any case, use plenty of weatherproof silicone sealant.
Mount the cantennas and access points outside. Use galvanized angle brackets, scrap wood, sheet metal and wood screws or lag bolts. Where and how you mount them depends on your particular building. Higher is better for better signal propagation. Try to mount under an overhang to provide a sheltered area for the enclosure.