Autovacuum does not stay turned off

We are attempting to turn off autovacuum but it keeps coming back.  We
can't afford the performance hit from vacuum while end users are
accessing our system.

Postgresql Version:  8.3.3
OS:  Linux 2.6.18-53.el5PAE #1 SMP

Running PostgreSQL setting:
sspg=# show autovacuum;
 autovacuum
------------
 off
(1 row)

pg.log Log Entries:
2008-08-26 15:24:50 GMTLOG:  autovacuum launcher started
-- and then we manually kill it
postgres 32371  0.0  0.1 1133768 23572 ?       Ss   15:16   0:00
postgres: autovacuum worker process   rollup_data_store
# kill 32371
2008-08-26 15:24:53 GMTFATAL:  terminating autovacuum process due to
administrator command

Does anyone know what will cause this bahavior for autovacuum?

Thank you in advance

-Jerry