Problem with timestamp - Pls help

Dear Friends,

I am using Postgres 7.3.4 on Linux server 7.3.

I wanted to update one column of my table with now() or timestamp. And I want that timestamp of format ------------------------
2003-09-19 18:39:08.13

To achieve this I have used the following

wats=# select now();
now
------------------------------
2003-09-19 18:39:58.62398+00
(1 row)

wats=# select substr(now(),1,22);
substr
------------------------
2003-09-19 18:40:01.25
(1 row)

wats=# select timestamp(substr(now(),1,22));
ERROR: parser: parse error at or near "substr" at character 18
wats=# select to_timestamp(substr(now(),1,22));
ERROR: Function to_timestamp(text) does not exist
Unable to identify a function that satisfies the given argument types
You may need to add explicit typecasts
wats=# select date(substr(now(),1,22));
date
------------
2003-09-19
(1 row)

Also I cant directly update my timestamp column as follows

update "WATS".users set to_rec_modified_date = substr(now(),1,22);

ERROR: column "rec_modified_date" is of type timestamp without time zone but expression is of type text
You will need to rewrite or cast the expression

Please help me with this.

Regards
Senthil Kumar S