Upgrading on RH72

Finally realized that the problems that I'm having are because my server is
RH72 running server 7.1.3-2 and my clients are RH73 running 7.2.1-5 and the
clients don't seem backward compatible.  So I thought I would upgrade the
server to RH73... OK that's not going to work.  So I grabbed the latest 72
rpms from a PostgreSQL mirror which have the version that looks like
7.2.1-2, so this should work.  Anyone have success with this?  I think it
said something about having to initdb...  what does this mean?

What does the PGDG stand for in the filename (i.e.
postgresql-7.2.1-2PGDG.i386.rpm)?