problem with access database

Hello

I use 1.12.0 PGAdminIII from a client for seven windows connect to a postgres server 8.4.2.1 installed on a Windows
2008server 32-bit server (service pack 2).  

I want to give access at the database "PicSaintLoup" to user "rihouet"

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If I configure pg_hba.conf with this line

"host    PicSaintLoup    rihouet        193.49.134.96/32    md5"

I obtain this message
" Error connecting to the server : Fatal : Aucune entrée dans pg_hab.conf pour l'hote "193.49.134.96", utilisateur
"rihouet",base de données "postgres", SSL inactif" 

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If I configure pg_hba.conf with this line

"host    postgres, PicSaintLoup    rihouet        193.49.134.96/32    md5"

It is ok

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I don't understand why I must make "postgres" in this line ?

Thank you

MCQ