WLAN w/in a LAN

What is the best way to create a WLAN within my LAN infrastructure? I want people to come into certain locations and get on the WLAN to get to the internet. Currently my users all have static IP addresses. They open a browswer and have to authenticate to a Web Security Server which then goes upstream to an ISA and then out the door. What might I have to have in place for a person to log onto the LAN and get on the internet by bypassing my internal LAN all together?