I'm creating a machinima in the halo reach graphics engine and there is a scene where the character bends down and picks up a key off the ground. However when I overlay the image of the key it moves with the camera as it pans, I want it to be still; Is there anyway to do this?
That's what tracking is for. Read up on it.
Mylenium
Here's where to start for 2D motion tracking:
"motion tracking overview and resources"
For the basics of the 3D Camera Tracker, see this.