Oh yeah, it's probably the 4GB of RAM
Well, that sucks, but you'll probably have to save jpeg versions of your PSD files in order to be able to place them.
No, not at all. That shouldn't make any difference.
Something is strange here. Why can I see a black shape in your layers panel thumbnail, but I can't actually see it on your image?
The best I can suggest is a brown Solid Color layer set to "Darker Color" blend mode, and painted on gently with a low-opacity brush.
But I'm not convinced it's necessary.
Oh good grief. Ignore that nonsense. They don't know what they're talking about either.
MUST you use this Fotofusion nonsense? Why not just make your collages in Photoshop like the rest of us?