Thanks very much for the hand-holding, Icarus. There's obviously something fiendishly clever going on in your system (is it Vista, perhaps?) which doesn't work in mine (XP Pro). If I click on the file name of the expanded image, the expanded image reopens, in the top LH of the screen, in exactly the same size - but the cursor doesn't do anything. So all I can do is Save and Open in a graphics program if I want to blow it up further. I wonder if in your system, and others, there is some automatic firing up of a graphics editor when you click on the file name
I'm very happy for those who have an easier route but I wish I knew why I can't do it myself!!
Chris