Shoutbox

its really easy..in messenger 2009 go to:

tools
audio and video setup
click next to go  video setup
under webcam dropdown menu select "disable"
done!

if you want to use your camera again just go back and select your camera from the drop down menu...no need to restart your computer!!!

I know this is different than what you are used to in messenger 8.5....in my opinion Microsoft drop the ball on this feature...hope this help!