UPDATE: Because I wasn't linking back to the sites where I got the code from, it might persuade people into thinking I'm taking credit for making the actionscript code, so here are the sites that I sourced from.
Big Fat Tutorial on Newgrounds: [link]
Flash CS4 virtual camera on Youtube: [link]
This file contains two cameras. One has actionscript 2 code, and the other has actionscript 3 code. Please note I didn't make the actionscript, I merely sourced it from around the internet. However I did make the camera in Flash.
What this "camera" does is force the stage to be whatever the camera object is covering, so when you publish the movie, you will see the movie through the camera object. You can also zoom in and out by resizing the camera, without having to touch your background.
The actionscript 2 camera is for people who prefer to use actionscript 2 in their Flash files. The actionscript 3 camera is for people using Flash CS4, and want to take advantage of the 3D positioning capabilities (which only work in actionscript 3).
Have fun with it.