I use OSX, when I download a movie prevue it works but full movies don't, how come? do I need to upgrade Quicktime?

Quicktime is fussy I find. Great when it works, but when it doesn't handle some of the files off gnutella too well (only showing the first few minutes, for example), the free opensource VLC player will often play the file right through.

Here's the link http://www.videolan.org/vlc/download-macosx.html

VLC works well.
I also have MPlayer OSX 2.
I don't know the reasons, but sometimes one will open something while the other won't. Quicktime is the least useful.
Good luck.

To open QT Mpeg 2 files you need to purchase the codec as as xtra. It doesn't come with QT. Even OS 9 QT player is better than OSX QT. You can play VCDs with it for a start.