Thanks Marie & Debbie!

Debbie, don't let X-11 put you off. There's nothing to it. Just install it and it will start when it's needed. Beware though, the GIMP has a terribly poor UI when you're used to Apple programs. I'd nearly be inclined to suggest trying the Pixelmator demo instead, and if you like it, buying that. Considering how powerful it is, it's very reasonably priced.

Bart.