Sorry, I had tried that also, though in my experience glass doesn't have *that* great an impact when you have a reasonable PC (I was a Vista technical adoption reviewer for my company so I've had a little experience with Vista.)
Anyway, just figured out what it was - I always install my apps onto a separate drive to make the apps semi-independant. So I just ran the dom3 exe from the XP install. This works for most apps and the registry entries/dll registrations are quite easy to re-create. Obviously didn't work in this case - re-installing under Vista did the trick. I guess the dom3 config file was linked back to the previous install?
Anyway, sorted now so I am happy
Cheers
Drew