problem trying to su - postgres

I'm a newbie to all things linux and have the following problem

running red hat linux 9 i log into my pc, change to su - and type the
password, all is ok and i get root(at)localhost <mailto:root(at)localhost>

I'm trying now to configure postgresql, which i installed with linux and it
says to su - postgres, i do this but instead of getting postgres(at)localhost
<mailto:postgres(at)localhost> i get -bash-2.05b$ , is this right? or do i
need to reinstall something / update something?

Using the graphical interface i've tried to add postgres as a user as it
doesnt show, but it says user postgres already exists.

An help would be greatfully received.

Thanks

Neil Thompson
Analyst/Programmer

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