update, truncate and vacuum

[Scott Feldstein <scott(dot)feldstein(at)hyperic(dot)com>]

Hi,
I have a couple questions about how update, truncate and vacuum would  
work together.

1) If I update a table foo (id int, value numeric (20, 6))
with
update foo set value = 100 where id = 1

Would a vacuum be necessary after this type of operation since the  
updated value is a numeric? (as opposed to a sql type where its size  
could potentially change i.e varchar)

2) After several updates/deletes to a table, if I truncate it, would  
it be necessary to run vacuum in order to reclaim the space?

thanks,
Scott