a question about dates and timestamp

hi all

i have a table like this

id_message      int4 not null default nextval (  ...
id_abonne        int4 
texte_message  varchar() not null        
date_message   numeric not null  

the default size of numeric is 30.6

another table :

id_message  int4
id_abonne    int4
text_message text
date_message int4


in both case date_message is used to store a unix timestamp ( number of seconds
since 1st of 1970)

for example : 965340000  = 2000-08-03 00:00:00+02

my question is how can i convert the numeric or the int4 value to a date value?

which function should i use to make something like this work ?

select convert_to_date( date_message) from my_table;

2000-08-03 00:00:00+02
2000-08-01 13:56:00+02
etc etc


thanks in advance

Pozzo Ange