You could try VHScrCap (http://www.hmelyoff.com/index.php?section=4) - it's Windows only at the moment but it's free and works fine with Flex for screen capture. I've done some work with it using Wowza Media Server to stream a user's desktop and it seemed to work ok.
- [flexcoders] Performing screen capture in Flex apps? Yair Flicker
- [flexcoders] Re: Performing screen capture in Flex ap... Steve Carpenter