Well, I may have some good news.
Having tried again this afternoon, it seems that what Blender 2.49b hates is my Magic Trackpad and Magic Mouse, and especially that I HAD them both connected at the same time.
I currently have no "ordinary" 3 wheel mouse so I think a quick trip to the shop MAY prove a worthy investment as once I disconnected my Magic Trackpad, Edit mode was not quite so unworkable. There are still legacy lines but no where near as bad as when I had the mouse and trackpad both connected. I'm hoping that a "simple" wired 3 wheel mouse will make things even better ... unfortunately, it's Sunday afternoon and the shops are closed. I'll keep you guys posted... meanwhile, I have a terrain to sculpt