Those that produce the things dont intend you to keep them alive after new year. they want you back next year for another one.

However I have mamaged to keep them alive quite sucessfully, though never got the red bracts back (thats the tricky bit

)
Basicaly just treat them like any other houseplant. Water but not too much or too little ant they should be fine. Dont expose to draughts or dry heat (ie from heating) though.
What you get is a fairly healthy (albeit green) pointsettia. As i said Getting the red bracts back for next christmas is tricky. It requires the patience of a saint to be exact. Never managed it myself so dont really know what it takes.