Thanks for the excellent tute arsheesh, it's very thorough and easy to follow.

It's mostly a simple conversion to photoshop; most of the commands are the same or very similar. The only tricky bit is that PS won't let you shrink a selection if your selection is the whole image for some reason (not sure if this is me or a quirk of PS). I had to expand the canvas bit by bit, first to the top of the neat lines, then to the bottom of the frame, then to the final canvas size, making paths along the way, in order to get it all in the right place.