I'm trying to build a website that allows my users to web chat via audio and video and I'm trying to do this using flash pro. Any idea of how I should start buiding this flash srcipt?
If you're unfamiliar with working with streams, the microphone, webcam, proxies, firewalls, web services etc etc, this isn't really worth your time.
There's plenty of boxed solutions and you should take a look at them, grab demos, experiment. To implement this would take even an experienced developer hours and hours of testing and developing with limited success (due mostly to web server limits and users machines, firewalls, users "allowing" flash to use their mic/cam, flash versions, etc).