It seems like a lot of other functions within ArcGIS are getting backwards compatibility (file geodb creation, MXD files). I'll still need to publish 9.3 PMF files for a few months and I couldn't find anything in the Publisher settings that would allow me to publish to a previous version. Is it possible?
Per this document (around halfway down, under the heading Saving from ArcGIS 10 to ArcGIS 9.2) you cannot publish a PMF for consumption via ArcGIS 9.2 if you're using ArcGIS 10. It does not mention this for 9.3, but if you're having difficulties reading a PMF in 9.3 that was published via 10, then that apparently doesn't work either (despite ESRI's not mentioning it in their documentation).
Their suggested workaround is: