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Did you install the perian formats? If QT loads the video but won't play it, that could be the problem. Can you save whatever QT tries to open and play it with something else?
 
If QTE fails to work for you, maybe PowerPC Media Center will work out. It's a small app (not really a 'media center') that can extract HTML5 video from websites and either save it, convert it to MP3 or play it through QuickTime Player. I use it for YouTube and many other sites all the time and it works a dream.

I like it, it works fine and will do the job for me on the rare occasion I need it.
 
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