Myst and Riven use older (Quicktime 2/3) codecs that only come with said quicktime versions. Thus, the best solution is to remove all versions of quicktime you have installed, then install the old version that comes with the Myst games, then install the latest quicktime 7 on top of it. Things should then work correctly for both old and new programs using quicktime.

And as Omecle said, Myst 5/Uru/Myst 4 are completely amazing, as are the previous Myst games in their own right.