help building datetime from varchars

Hopefully someone can point me in the proper direction....

I have a table containg (amongst others) two varchar attrs date_s &
time_s.

They contain strings like:

date_s | time_s
------------+----------
01/10/1989 | 00:30:00

Can someone suggest an sql to turn these into a single datetime?

I have tried the following with results I don't understand:

env2003=# select date_s || time_s, to_timestamp(date_s || time_s,'DD/MM/YYYYHH:MM:SS') from event limit 1;
?column? | to_timestamp
--------------------+------------------------
01/10/198900:30:00 | 1991-06-05 00:00:00+12
(1 row)

env2003=# select date_s || ' ' || time_s, to_timestamp(date_s || ' ' || time_s,'DD/MM/YYYY HH:MM:SS') from event limit 1;
?column? | to_timestamp
---------------------+------------------------
01/10/1989 00:30:00 | 1991-06-05 00:00:00+12
(1 row)

Thanks,

Brent Wood