Quicktime problem driving me nuts

I'm at a friend's place, and she has an old graphite imac running old 10.2...

(this could indeed be the problem!)

Whenever she hits the quicktime trailer site, or other sites with movie or HD links, she's unable to play the movies, and is told:

"You may experience playing video track in 'iron man superbowl (eg)' because the required compressor could not be found. Would you like to close or continue?"

Now the extent of my computer know-how runs to downloading a pack of filters & codecs and copying them into the Quicktime folder, but this hasn't worked.

Anyone have any idea?