Hi Roger,
As Owen indicated,
http://www.projectpluto.com/guide8.htm#hard_drive
gives gory details of how the installation of one or both CDs is
handled. The gist of it is, almost any configuration of installed
data is possible (and fairly straightforward).
The million-galaxy catalog(ue) is on the second CD, and by
default, it isn't even shown. It sounds very impressive, and in
some ways it _is_ very impressive. However, for most uses,
the 190 000-object PGC is the way to go. Its data has been
checked more thoroughly, and it gives more information about
the galaxies, and... well, let's face it... few of us will be observing
galaxies much fainter than the PGC limit.
-- Bill