[Sunny Thaper]

If you render the avi in too high a resolution/quality, it will most certainly slow your pc down. What you can do is download a low overhead codec like www.divx.com or render out in quicktime, both provide very good means of low overhead videos. Also, about your weird lighting thing, it could be because of the quality of the avi itself too. Lots of weird artifacts can appear in low quality avis.