Changing user passwords

Hello,

Is it possible to change a user's password without using the pg_passwd
command?
For example, how does a user changes his password from the interactive
monitor?
In case you were wondering, I'm scripting an interface to a pg database
using
Perl/DBI and the "administrator" web user should be able to change the
default
password.

I'm a pg/SQL novice, yet I'm always willing to learn new things,
references to 
documentation will be appreciated as much as solutions.

Apologies in advance for my ignorance.
-- 
Rob van der Leek
E-mail: rob@frog.nl
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Tel. 030-2440550
Fax. 030-2440700
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