I have ActivePerl 629 - which I compiled, so PPM would be the one that comes with build 628.
I'll try on some other machines and see what happens. But I was looking through the PPM.pm source and it implies that repositories can have "Summary" files. These summaries somehow aid the search routines. I am guessing that PPM::SOAPServer is a SOAP service that acts as the repository and searches the PPD files returning descriptions etc that match the search. But maybe I have the wrong end of the stick!