After uploading movies and trying to play them, I often recieve error messages. "Because its a file that quick time understands" or Need a v7 format on windows media player. I have a brand new updated version of both and also quicktime pro. So why do I recieve these messages, and is there any thing I can do to sort these problems?

VLC will usually do the trick: http://www.videolan.org/vlc/ (has built in codecs for most video formats)
& choose any mirror site they're all english versions! Or else mplayer: http://mplayerosx.sourceforge.net/

Thank you very much for your advice, I will try it and let you know. Very impressed with the speed in which you answered my question.

Regards