Some video codecs support Poser's alpha channel. I'd recommend Huffyuv or Lagarith, but I'm not certain that After Effects can read them properly.

Alternatively, you could import the video background into Poser and render your figures on top of it.

And please STOP SHOUTING WHIT THOSE CAPS "big letters"....

We'll simply have to outshout him, BARTWORX ....