Just install AOLServer and Postgres on the 2nd box, make sure it works but
point it to the postgres server on the 1st box. Make sure the 1st box backs
up the database to the 2nd box daily (You don't have to restore it, you just
need a backup of it on there.)
Now you have the 2nd box that can handle your mailing load and take over
some of the web load and, if box 1 dies you can restore the database backup
that is already on box 2, start postgres, point aolserver to it, and you're back
up and running with minimal downtime and the loss of less than a day's
worth of data.
