This was already mentioned by Shane Jensen
http://www.sonycreativesoftware.com/forums/ShowMessage.asp?ForumID=4&MessageID=705602at the end of this thread,[/link] but I believe it needs it's own thread so that people don't miss it.
The latest version of Quicktime works just fine in Vegas 9d. I just updated to the 64bit version of iTunes in order to bring both iTunes and Quicktime up to date and give it a shot. It works just fine. No more black instead of video. I guess it was a Vegas issue after all! Who'd have thought we were all wrong.
Anyway, if you haven't updated your Quicktime version because of this issue, you can now.