Wireless channels overlap ?
The 802.11 b/g WiFi standard defines a total of 14 frequency channels. The FCC allows channels 1 through 11 in the U.S., and most of Europe allows channels 1 through 13.
WiFi channels actually represent the center frequency that the transceiver uses (e.g., 2.412 GHz for channel 1, 2.417 GHz for channel 2, etc.). There is only 5 MHz separation between the center frequencies, and the signal occupies about 22 MHz of the frequency spectrum. As a result, an 802.11b/g signal overlaps with several adjacent channel frequencies (by 11MHz on each side of the center frequency). This leaves only three non-overlapping channels: 1, 6, and 11 in the U.S. to use without causing some interference between access points.
The best approach when choosing a channel is to do a site survey from your wireless client computer (info), or the router/access point (if available). Note the channels of nearby wireless networks. The default on many routers is channel 6.
Once you have a site survey available, just keep in mind to use non-overlapping channels (1, 6, 11), or minimize overlap of signals by using channels as far apart as possible from other networks in range. You can experiment by checking signal level when you configure your access point on a certain channel as well. This may be important in fine-tuning for the best possible signal, as some channels may experience interference from other sources that are not detected as neighboring networks.