Charlton,
In the IPTC/XMP preferences in PM, do you have the "Write IPTC as Unicode" option checked? If so, this could be the issue since Photoshop doesn't understand Unicode IPTC (although they do understand XMP of course which is Unicode). I don't know if this issue ever got fixed for PS CS3 or not (we alerted Adobe about it some time ago). So your options would be to uncheck this box or embed XMP (perhaps only XMP).
But Kirk is right - please look at the File Info in PS to see what it shows.
--dennis