I just aquired a ten-second HD 1080 file (1920x1080 .mov file) and tried opening it in Vegas 6 and Vegas doesn't seem to like it---I can't open it or even place it on a timeline.
1920x1080 is a resolution (that Vegas has no problem with), ".mov" is just a wrapper that can contain video and audio encoded in any of many different codecs (that Vegas can handle if you have the codecs on your machine).
Start by opening the clip in your QuickTime player and check the properties of the clip. This should tell you a bit more.
I recently had a struggle with a Quicktime-format HDV file from a Mac, not working with Vegas 7. Even though it was supposedly QT format, the Apple QT player (on my WinXP box) could not play it either.
However VLC Media Player was able to play the file, and eventually I was also able to use VLC to transcode it to MPEG2 that Vegas could use. I have found VLC is the most general purpose player, handles the widest variety of formats. VLC is a free download from http://www.videolan.org/vlc/
Note: While VLC is playing a file, type control-I and click on the "advanced information" tab and it will tell you the name of the audio and video codecs.
If this was HDV captured on a Mac there was a recent post from Sony regarding trying to get these files into Vegas. Even though you might find a way it seems the quality will not be so good i.e. not worth the effort.
HDV captured on any other system was claimed to be fine.
I struggled with this some time ago, in the end I just did a PTT from iMovie and captured the tape back into Vegas. Thankfully it was a very short project, not the most elegant solution I know.