Some useful links about video in Flash:
Adobe Flash Video developer center:
http://www.adobe.com/devnet/flash/video.html
Article on video encoding:
http://www.adobe.com/devnet/flash/articles/encoding_video.html
Article on selecting a video encoder:
http://www.adobe.com/devnet/flash/articles/selecting_video_encoder.html
Article on using the Adobe Flash CS3 Video Encoder:
http://www.adobe.com/devnet/flash/quickstart/video_encoder/