FW: [NOVICE] Creating a new server

I have an old server that is still working faithfully. It is running Red
Hat 7.2 and Postgersql 7.2. In anticipation of the day it will die, that
I am concerned is closer than I want it to be, I have set up a shinny
new server running Red Hat Enterprise 4.

I am trying to migrate the database from the old server to the new.
Until I get things up and running on the new server, I do not want to do
anything that I fear may cause damage or stop the server from working.
This includes a re-boot. I am interested in the least impacting
migration strategy.

I tried
>pg_dumpall > sync-up.db
Connected to template1...
Psql: FATAL 1: user "jcarlson" does not exist

I then tried
>createuser jcarlson
Psql: FATAL 1: user "root" does not exist
Createuser: create of user "jcarlson" failed

I have found that I need to change the pg_hba.conf file to change the
authentication mode. In the document it says I need to do a pg_ctl
reload. How impacting will this be to the processes currently working?

As stated earlier, everything is currently working. Is there a way to
pg_dumpall or transfer the database without being a user or having to
reload?

Any suggestions on how to carefully transition this to the new server?

Thanks,
Jim Carlson