ok, what video-card and sound card do you have? and is it 32bit or 64bit? (just a little more about your computer specs)
usually, re-emrging the media player (VLC, mPlayer, xine, or gstreamer) can help, but appearently it is a hardware problem since it didn't work in other distros.
also, when you play these videos, is beryl, or compiz on or not?
Ignorance is not shameful. Arrogantly ignoring and denying your ignorance is.
All men are capable of learning, except two: The Arrogant and The Shy.