I had asked in another thread whether I could download and install the current tryout version of PM, and then use my old serial number from a PM 7 upgrade I had registered with Adobe back in 2002. I was under the impression this process would work for InDesign, or at least since ID required "activation," but PM dates to another era and my memory is not that good. No one answered, so I went ahead and installed the Tryout, and can now report that the Tryout version does not allow conversion to the full version by adding a valid serial number; in fact, the Tryout installs itself in a special Tryout folder, suggesting that it expects to be un-installed before the full version is installed.
I kept searching through old stuff and eventually turned up my original PM 7.0 CD -- an upgrade -- but not the carton it came in. I uninstalled the tryout, installed PM7.0, and found that because it was an upgrade I needed a valid serial number from an earlier PM. The only serial number on Adobe's cardboard sleeve for my PM6.5 Plus was for the bundled Photoshop, but having registered my purchase with Adobe I could still retrieve the number, a string of 15 digits. PM 7 upgrade rejected this, as well as the 15-digit serial number for PM5 (not to mention the PS serial number from my PM6.5 CD).
I had done a cautious un-install of the tryout: when the un-install process said there were elements that might possibly be shared with other programs, I let it preserve those lest I disrupt the CS2 software I still use occasionally. After my valid serial numbers were rejected, I threw caution to the wind and re-installed the tryout so I could zap it completely. Not surprisingly, the re-installed tryout found traces of its previous incarnation, reporting I had just 7 days remaining in my 30-day trial (I thought I'd started the day with 8). I un-installed again, this time telling it to take everything. I then tried installing my PM7 upgrade again, and this time it accepted the serial number from my PM5 carton: the same 15 digits preserved in Adobe's registration, but this time broken up by hyphens, NN-NNNN-NNNNNNNNN. I think I had tried the hyphen-less version first, and thus that the hyphens made the difference, though they key may have been the complete un-install.
A quick test of suggests IDCS2 is happy as ever on my XP machine. Perhaps I should add that I have carefully avoided upgrading the OS to XP SP3, dimly recalling that SP3 can complicate ID's ability to read PM files. For what its worth, I turned up the box for my Mac PM6 which shows the serial number as a single string of 14 alphanumerics, two of which are letters.
InDesign CS2 will not be able to open PM files on XP SP3, Vista, or Win 7.