Try changing your WiFi channel. There are three discreet channels - 1, 7 and 11. (The other channels overlap each other.) You can download and install a program called Airsnort which will tell you what WiFi access points it can see. See if one of these three channels is clear. If it is, change to that channel. Your WiFi radio in the computer will figure out the channel automatically so there is nothing to do on your computer's end.
Channel 7 is the default for almost all routers so it's very common for your neighbours to have APs on channel 7.
The other issue is where your AP is located. WiFi, like any radio transmitter, works better if it's mounted high. If you have it on your floor or in your basement, you'll get less signal perpetuation than if it's mounted atop a bookshelf or on the upper floor of your home. (One caveat: if you're directly below your AP you'll tend to get very bad signal as the broadcast is out and down, but at an angle.)