yes this is possible.. it is very hard to get it right.. havaen't really had it working 100% correct yet... But i haven't used much time on it either thou... It is advised that you take out your normal/real webcam out of your computer... This way I got it working partiatialy... I started a webcam convo with my friend, and I could see in my own webcam window the part of the screen... but as soon as he accepted the cam it stopped working and said that I had no camera connecting... Just use some time playing with it.. finding some settings to trick msn messenger into beliveing you still have your cam connected or something like that.. It should be possible...
...
Edit:
Btw, the way to active this is start camtasia studio, then start the recorder.. go to tools > options... find the tab live.. and then "Enable Live Output".....
...