Problems installing 7.4.2

With a dying hard disc, I backed up my db files from 7.4.1 and installed
7.4.2 on my new disc after installing Fedora Core 1. Two problems:
   1.  User postgres seems to have been set up automatically, and I
can't find a password that works.
   2.  When I try to start psql under my own username, I get
        "file /usr/lib/libpq.so.3 from install of
postgresql-libs-7.4.2-1PGDG.i386.rpm conflicts with files from
postgresql-7.3.4-2"
How can I fix this short of wiping everything out and starting over?