Buying my first projector soon, so what do I need to know about projector screens? Basically I'm planning on a DLP projector, and I'll be watching in complete darkness in a light controlled room. I'll be sitting directly in front of the screen, so I want light to be reflected straight back at me, and not spread out. Any good sources on the net for learning about this stuff? What kind of money are we talking about for a good one?