Couple of Possibilites,
1. Try rendering the full movie.
2. or Render 1 light source to the clip and render to a new movie. Render 2nd light to new movie and create yet another new movie then render final light to that.
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.