Upgrading from 7.4.19 to 8.3.1

Hello All

We are upgrading from Postgres 7.4.19 to 8.3.1 and wanted to know as
for Tuning the database what options in the postgresql.conf have changed
or have been added that I will need to adjust. Example shared buffers,
sort memory and vacuum and others. Also we are planning on using
autovacuum and would like some input on what other users on the list are
doing. I know this a vague question. but I see many differences between
the two config files and wanted input.

Thanks

John Allgood