slow vacuum performance

Hi,

I am running pg 7.4.1 on linux box.
I have a midle size DB with many updates and after it I try to run
vacuum full analyze.
It takes about 2 h.
If I try to dump and reload the DB it take 20 min.

How can I improve the vacuum full analyze time?

My configuration:

shared_buffers = 15000          # min 16, at least max_connections*2,
8KB each
sort_mem = 10000                # min 64, size in KB
vacuum_mem = 32000              # min 1024, size in KB
effective_cache_size = 40000    # typically 8KB each
#max_fsm_pages = 20000          # min max_fsm_relations*16, 6 bytes each

#max_fsm_relations = 1000       # min 100, ~50 bytes each


regards,
ivan.