Yea, I don't get this one either. Get Info (apple-I) on these files shows them as MPEGs which Quicktime is -normally- able to play.
It's a mystery...
But, don't throw these files right away. First, dld and install VLC player which is a great player (although a little slower and more buggy than Quicktime IMO) and can play many many file formats that Quicktime can't. To get it, Google VLC or simply go to www.videolan.org to get it. It's free and it's great. It even manages the Ogg Vorbis format (although I find that the step forward/backward functions with this format are pretty screwy).

Edit: Ooops. I probably was writing this post at the same time as me Lord.

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