I have seen the comments about using Alpha Channels with Keying out Backgrounds etc.
What I want to do, is to create a video for the web that you can see the background of the webpage through. I have seen some spokespeople videos "walking" onto a webpage without a background and I wanted to try and duplicate that if possible. Is this an After Effects effect? or Flash using a transparent window? Flash doesnt take .avi files so I was wondering how I make that happen.
You need to encode your video in FLV format with an alpha channel. Either by exporting directly with AE in FLV format+alpha, or in another container that supports alpha and the encoding it with Flash's encoder.
Then your web code will need to display flash in transparent mode.