When implementing multiple 802.11b/g wireless access points, the most important consideration is picking which wireless channel to use.  Depending on where you are in the world, the full range of channels is different, but in the United States, the available channels are numbered 1 through 11.  Many modern access points dynamically pick a channel when they first boot up, and most of the rest of them come with preconfigured default values.  A small minority, mostly enterprise devices, come with the wireless interface disabled until it is configured by an administrator.

It might seem like a good idea to dynamically assign channels, but it can quickly get you into trouble and result in less than optimal performance on the network.  The problem arises from the fact that the individual channels actually overlap each other and can cause interference with each other.  Assuming you are in the United States, you can implement no more than 3 of the 11 channels without any overlap: 1, 6, and 11.  While this may seem very restrictive if you need more than 3 access points, you can ordinarily design your network in such a way that you can stagger your access points so that they do not interfere with each other.  If you absolutely have to use more than 3 channels, the next most efficienct layout would be using channels 1, 4, 8, and 11.

The next consideration that you must be aware of is that you cannot have 2 access points next to each other with the same channel.  What happens if you have 2 access points with the same channel next to each other?  Two things, actually: 1) They see each other as interference which degrades performance, and 2) You will be unable to roam from one access point to the other as you move around.

Finally, all access points in the network must have the same SSID and encryption settings.  Always remember that SSIDs are case-sensitive.

If you have chosen to use multiple home-quality wireless routers instead of purchasing units that are only wireless access points, be sure to disable the DHCP server on all of them except for one.  Also, make sure to only use the Internet port on the wireless router that is plugged into your Internet connection... on all other routers, it will remain empty.