Problems Testing User-Defined Function

Hi list,
I'm a newbie and I have a problem. I've defined the following function using
pgAdmin but I am clueless as to how I can test it. I will eventually be
calling this function from a .NET application but I want to test it using
raw SQL first. Here's the function definition:
CREATE OR REPLACE FUNCTION sp_insert_manifest(_sender varchar(255),           _sender_email varchar(255),
_reply_tovarchar(255),           _filename varchar(255),           _file oid,          _datetime_sent timestamp)
RETURNSinteger AS $$
 
-- blah blah --

$$ LANGUAGE plpgsql;
I am trying to pass the following values to the function but I have been so
far unsuccessful.
SELECT sp_insert_manifest('me', me@you.com', 'me@you.com', 'test.txt', NULL,
'2006/06/09')
Can anyone help me here?
Thanks,
Rommel the iCeMAn.