I've run into the same problem. Oddly, it (jpeg inversion) happens on one Mac platform (GR Powerbook) but not on another (G4 tower) running same OSX and software. Whether the inversion happens or not also seems to depend on the particular application that produced the .pdf file that Acrobat opens, and then converts to .jpeg. The inversion happens when Illustrator 10 generates the .pdf but not when Macpstopdf generates it.

I wish Adobe would look at this and find out what's wrong - and give us a proper solution. I'm loath to spend $39 for the privilege of pointing out this problem to them and asking them how I can fix it. Especially given the money I've already spent for their software.