Thanks very much. Unforunately I know very little about the various literature out there, I've never read a 'how-to' manual in my life. What you see there is a cumulation of years of guess work.
I used Paint Shop Pro rather than Photoshop, but both packages use similar techniques, albeit with a different layout.
Tips? Probably the best thing to do would be to find an image and experiment with editing out various parts of the image, eg. a fence in a field, a man on the street, etc., using the clone brush (not sure if it's called the same in PS, someone will be able to confirm that. Play around with creating a scene by cutting people out of an image and pasting them into a diferent background, trying to make it look as natural as possible. When doing that it's often good to use the soften tool around the outline of the thing you've cut and pasted, to stop it looking too pixelated.
As I say, all I know came from building up bit by bit and experimenting (kinda like most of my pc knowledge actually). If you don't know what a tool on the menu does, try it! Master each tool, and each setting of density, hardness, build-up etc seperately. The clone brush will be the hardest to master, when getting subtle shades it's a case of reducing the opacity right down and build up bit by bit.
Hope this helps a bit.