Java/Swing programming question

Update: A custom paint() jobby seems to work splendidly for this, and there's no thread necessary, it just draws it properly. (in fact, when I tried to use a thread to update, it threw strange exceptions). Now I just need to get the blasted side-panel to update, too. That might actually be easier to crack, since I got something reasonably similar to work in the map editor.

Thanks for all of your help, Dabz!