Well the thing about mic cable for data transmission like DMX is, it works.......until it doesn't. I would urge you to start using DMX cables in the near future.
Far as I can tell there is no currently known issue with Windows Vista. and since it only happens on that computer, to me it seems like the drivers for the interface don't like something on that computer..... question is, what?
My email is jamesk at Americandj dot com