Interesting that I should use the analogy of projections on the screen. Geshe Kalsang, who is teaching us the Seven Points of Mind Training this weekend, used exactly the same example. This is a line of thought used in the Mind Only School. Nothing exists except as projections of our mind. He reminded us that when you go to a movie, you watch the images on the screen, you get so involved, you feel the emotions...But they are only images projected on a screen. There is actually nothing on the screen itself! After all, it's only the play of light.
The Madhyamika-Prasangika school is more subtle than this. Things do exist, in a conventional way. We agree to their existence. Was it Berkeley who kicked the stone and said, "Feels real enough to me..."? Something is there. We feel it, we hear it, we smell it, we taste it...We label it. ie. give it a name. It's just not there in the way we think it is.
In what way is it there, then? Ah, that's the 64k question. The answer lies in the extended analytical meditation you are supposed to do, always questioning your perception of phenomena. The primary phenomenon to question is your self. Your concept of "I".
A "simple" question to start with. When you think of "I", where is it, exactly?