I'm teaching Photoshop 5 to a group of 1st Year Industrial/Transport/3D Designers at the moment. It's only when you try and teach it that you realise how much there is to it. I mean…where do you start? The problem is made more tricky by the fact that the group is at different levels of expertise. I ended up starting with what a pixel is, then stuff about the differences between images on screen and on print and then on to layers and the good ol’ ‘acetate metaphor’. I then proceeded with the most important stuff: how you can ‘modify’ existing images of people by adding hilarious mustaches, giving them three eyes and humungous ears etc… what fun.