Using chkpass() in a query

I'm trying to perform an SQL statement to extract usernames and crypt'd
passwords from a database table, and am running into difficulties with
chkpass. I can run it just fine in a straight query, but when I try to use
it on a column from an SQL statement I get an error.

scamp=# SELECT CHKPASS('foo');
chkpass
----------------
:Zbcg0W4wPBNBU
(1 row)

scamp=# SELECT CHKPASS(Password) FROM EmailAddress;
ERROR: Function chkpass(character varying) does not exist
Unable to identify a function that satisfies the given argument types
You may need to add explicit typecasts
scamp=# SELECT CHKPASS(Password::TEXT) FROM EmailAddress;
ERROR: Function chkpass(text) does not exist
Unable to identify a function that satisfies the given argument types
You may need to add explicit typecasts
scamp=# SELECT CHKPASS(Password::CSTRING) FROM EmailAddress;
ERROR: Cannot cast type character varying to cstring

Does anyone have any suggestions on how I could accomplish the above?

--
/* Michael A. Nachbaur <mike(at)nachbaur(dot)com>
* http://nachbaur.com/pgpkey.asc
*/

...[Arthur] leapt to his feet like an author hearing the phone ring...