Not sure if I've misunderstood you but first point I'll make about your feed diagram is that the optical from your dvd player is for sound only. That's a fine way of connecting to your amp but It won't allow you to take the picture out of your amp.
I personnaly wouldn't take the picture through the receiver. It is probably the cheapest option. s-video is OK but when projecting onto a 7ft screen I saw flaws in the picture which I wasn't happy with. I found component much much better (got that through a scart to component conversion box).
You could connect vcr and dvdplayer to a scart switching box (Quattro+) Take the feed out of there (scart) and into a "scart - component" switch box then component cables straight into projector. And do the PC as you said.
If you pick a good retailer they should be able to sort you out pretty easily. I recommend Andy at
www.av-sales.co.uk he loves connection issues
My Z1 can to 1024 and also 1280. Not sure about the AE100.