Table UPDATE is too slow

 We have a web based application with data that is updated daily. The
biggest bottleneck occurs when we try to update
 one of the tables. This table contains 58,000 rows and 62 columns, and
EVERY column is indexed. Every column is
 queryable (?) by the users through the web interface so we are
reluctant to remove the indexes (recreating them would
 be time consuming too). The primary key is an INT and the rest of the
columns are a mix of NUMERIC, TEXT, and DATEs.
 A typical update is:
   UPDATE dataTable SET field01=44.5, field02=44.5, field03='Bob',
     field04='foo', ... , field60='2004-08-30', field61='2004-08-29'
     WHERE id = 1234;

 Also of note is that the update is run about 10 times per day; we get
blocks of data from 10 different sources, so we pre-process the
 data and then update the table. We also run VACUUM FULL ANALYZE on a
nightly basis.

 Does anyone have some idea on how we can increase speed, either by
changing the updates, designing the database
 differently, etc, etc? This is currently a big problem for us.

 Other notables:
   The UPDATE is run from a within a function: FOR rec IN SELECT ...LOOP
RETURN NEXT rec; UPDATE dataTable.....
   Postgres 7.4.3
   debian stable
   2 GB RAM
   80 DB IDE drive (we can't change it)

   shared_buffers = 2048
   sort_mem = 1024
   max_fsm_pages = 40000
   checkpoint_segments = 5
   random_page_cost = 3


 Thanks

 Ron