The only way to import an AVI, MOV or whatever format into your Poser scene is as a background.

Your best bet is to do this in post production. I would set the material color of your TV screen a bright blue or green (using the same color as your ambient color) and then use an effects program, such as After Effects, to composite in the AVI of what's on TV. This could get complicated if your camera is moving in the living room scene.