Did you try what was suggested in the existing Vista threads? ( [Windows Vista) )
I'm not sure myself as I've never tried to run Opus 8 on Vista but it looks like there's some info in those threads.
Of course, these problems will be gone in the next version since it adds proper/official Vista support. That version is being beta-tested now (by Jon, Tanis, myself and some other forum members running Vista on our main machines) and the wait should be over soon.