any way to remove a password?

Is there any way to remove a password, specifically from the postgres
user? I installed the 8.0 Windows version via the installer, and it
forces you to set a password. I'd like to reset this so that there is
no password (basically, to match the setup on several other machines -
and no, for a number of reasons it's not feasible to just set
passwords on those other machines).

I know about the alter user command, but I haven't seen a way to use
it to remove a password. I've tried:

alter user postgres with password '';
alter user postgres with password null;

The first one doesn't work and the second returns an error.

Does anyone know whether this is possible? Thanks.

Neil