Did you finalise the disk after copying the files across? If you used Roxio's drag and drop and failed to finalise the disk you may have problems.
I don't know what effect it will have on the files if you try to finalise in Vista.
Try the Roxio Community, see if anything matches your situation.
http://forums.support.roxio.com/topic/64293-accessing-files-on-unclosed-disc/