The quick install doc says the following in the
"Changing Administrator Password" section:
Log into MyPBS with your favorite web browser at:
http://my-server.mydomain.com/mypbs. Log in with the
username admin with the password pass. Now you will be
forced to change your administrator password.
In the install I did I was never "forced" to change the
admin password. Now I did not have a .htaccess file and
did not have mod_rewrite module loaded the first time I
logged in as the admin user either so that might have
had some effect on that.