many row updates

Hi!

I have table with row named rank and some other rows. I have about
900.000 rows in table and I need to update
all rows with the same value of rank, so I run update table set rank = 1;

The only problem is speed. I'm waiting about 30 minutes and it's still
running.

My system is pg8.1 with one SATA HD and P43GHz

I think there must be some configuration option or something to be
update so slow. I also remove index from this row but doesn't help.
Maybe somone have an idea what parameter to tune or what can I check to
see why the update is so slow.

regards

Uros