Adding a wireless access point to your network provides a great convenience for those with wireless equipped notebook or handheld computers, but adding wireless can also create many security issues. In addition to the usual wireless security advice--disable SSID broadcasting, change the default settings on the WAP, use WEP or WPA encryption--another security measure is to isolate the wireless clients from your wired Ethernet LAN by creating a separate segment for them.
Here's how: Your firewall should have three or more network interfaces. One is the external interface to the internet. That leaves two internal interfaces. Plug a switch for your Ethernet computers into one, and plug a switch or hub into the other, into which you'll plug your Wireless Access Point.