Sorry TeaSpoon, that's not what he's asking. He's wanting to take what's being rendered and turn it into a video that can be played back. Like all those video game videos on youtube.
Lavaman, you can use fraps as Big Man suggests, but it requires registration. If you want to do it without having to pay any money to get full features, you can try Windows Media Encoder. Although I do not recommend WME unless you don't mind the fact that you won't be able to transcode it to divx, xvid or the like.
Also, you'll need a dualcore or hyperthreaded CPU inorder to do this because otherwise it'll suck up too much of your CPU and you'll trash your framerate to absolute crap while the recording is occuring.
I actually used to run a live video stream of what was going on inside Second Life for Second Life's main webpage. Back then, I didn't have a dual core CPU, so what I did was I got out an ancient computer from the closet and slapped a cheap $25 TV capture card in it. Then I plugged my system's TV out into the other system's capture card. That completely offloaded the movie creation to the other system and let my computer render Second Life contentedly.
No matter where you are... everyone is always connected.