I work for a non-profit and I just upgraded to InDesign CS6 on my (signifcantly more robust) machine. Now thier (significantly wimpier) machine needs to be upgraded too as we send INDD files back and forth on a monthly basis, and both sides do edits to the file. The INDML file I export out of CS6 is greying out many of the linked photos (but not all) when they read the INDML file in with CS4.
1) Upgrading the slower machine to CS6 is the place, but the hitch is that computer has a graphics card that is only OPENGL 1.5 capabale (GMA X3100). The CS6 specs state you need a card that supports OPENGL 2.0. We can't afford to replace the computer, so: I wouldn't dream of running photoshop CS6 on this old machine, but could InDesign CS6 function on OPENGL 1.5?
2) Alternatively, why are only some of the pictures greying out in the INDML file? Can I fix this CS6 > CS4 issue without upgrading to CS6?
The system requirements for stand-alone ID don't mention OpenGL at all. You might want to download a trial and see how it runs.
.idml does not include any link previews (that's one of the main reasons the file is so compact). Images that are showing up on the other end must be accessible so that ID can regenerate the previews.