timestamp with postgresql 7.3

Hi,

I have a table a field with timestamps in seconds since epoch and I would
like to get a human readable date... but it seems that postgresql 7.3 does
not support the datetime(), timestamp(), timestamptz() functions...

I tried the example in:
http://archives.postgresql.org/pgsql-bugs/2002-07/msg00117.php

and get:

DB=# select val, datetime(val), "timestamp"(val), timestamptz(val) from test_table;
ERROR:  Function datetime(integer) does not exist       Unable to identify a function that satisfies the given argument
types      You may need to add explicit typecasts
 

And tried various typecasts without any success.

Any help?

---
Claude