Big database problems

Ok, here goes...

I have a pretty big database (total 20 gigs) - several tables have many
millions of rows.

We're running 7.1.3 and I know there were a lot of improvements in VACUUM
and it's handling from 7.1 to 7.2 but sadly we can't upgrade at this time..

We're hanging on our VACUUM ANALYZEs now, and while it's understandable that
it's really slow (this box is absolutely stomped) it doesn't appear to be
doing anything (it's using all the processor but nothing more has been
written to the debug log for hours).. Just last night the database grew
moderately but it only took 3 1/2 hours to VACUUM ANALYZE the entire
database. The 1 table analyze has been running over 5 hours now.

The table it seems to be hung on is 4 gigs (80 million rows of 2 int4
fields), the primary key index is 3 gigs and the secondary is 2 gigs..

This table is constantly being added to through the day, so what happens to
all those inserts while it's being vacuumed? I assumed they would interfere
with the vacuum but it seems that they haven't yet as this is the first time
this has happened since I have been here.

Any ideas of where to look or what to do?

Thanks!!!!

-Mitch