A lot more info is needed to give you a proper response.
Is the shot fixed, moving or handheld?
Is the object to be removed moving or still?
Does the object pass in front or behind other objects?
Posting a still from the footage would be very useful.
Tools that may or may not be used for such a task include the Clone Stamp tool, Masks, and Motion Tracking.
As Andrew said, we've got to see the shot. You can remove something by masking, but then you've got to fill the hole. I've done this several times but we planned for it when shooting so there was a clean plate without the actor available to fill the hole. If you haven't got a clean plate or some portion of the shot whithout the person in the shot it's going to be very difficult to fill the hole.
Unfortunately it's about as hard as it can get. It's a handheld shot, the person that needs to be removed does not move in a way that would allow Motion Key to work, and the person is partially obscured by the two subjects of the shot, and the hair of one of the subjects.
http://vimeo.com/27863827 The password for the video is ccolton.
The highlighted person is the one that needs to go.
Removal would take hours. First step, stabilize the shot so the only thing moving is the subject. Second step, roto as best you can. Third step, clone or duplicate some other part of the footage. Final step, remove the stabilization to put the camera movement back in.
It looks like there has been a family row. The only other option that I can think of would be to follow the same steps as above except roto out the foreground and then apply some kind of effect like a blur or a glow and a blur to simulate a shalow depth of field and heavily stylize the shot. It would be much quicker than the cloning/replacing option.
Unfortunately I have CS4, so no rotobrush. I'm considering going to CS5.5 soon though. Is it worth it?
Back on topic, I might try the idea of simulating a narrower DOF. Can someone point me to a good general rotoscoping tutorial for AE? I've done some motion tracking but nothing this complicated.