These problems are almost certainly driver issues, especially if the video is being displayed using the chromakey feature. Try switching to on top and/or turn off video embedding.
Obviously Opus v5 has grown up on XP so we probably can't expect Vista to accomodate it flawlessly but in our experience the real issue with Vista is driver support and system performance issues.
A laptop which ran a 200 Mb opus presentation for one of our clients without problems barely scores a 1 on the Vista performance index and now blue screens if you try to run Vista
And publishing the publication under Vista isn't going to help that either I'm afraid.
Paul Harris