auto vacuum, not working?

Hi,

yesterday I delete about 200 million rows of a table (about 150GB of data),
after delete completes the autovacuum process start.

The autovacuum is running for about 11 hours but no space is released

Autovacuum parameters are with default values in postgresql.conf

The postgres version is 9.0.3

The pg activity reports:

select (now()-query_start) as duration, waiting, current_query from
pg_stat_activity where current_query ilike '%auto%'

10:42:19.829 f "autovacuum: VACUUM ANALYZE
public.myTable"

How can I release the space used by deleted rows? Without block the table.

Thanks!