ALTER TABLE and dropping a column

7.1 at least doesn't seem to support a 'DROP COLUMN' command as in

ALTER TABLE foo DROP COLUMN bar;

Is there a way to do that manually and safely, e.g. by manipulating
pg_class or pg_attribute? I found a couple of threads about it dating
from way back in summer 2000 and early 2001, but nothing conclusive.

Thanks, Frank