I have no experience of this software, but the document that you linked to is horribly dated, and a lot of things in it are not correct for Red Hat 9. I would contact the manufacturer for newer docs, because if this the latest doc then they are doing a very poor job.
You can add users and groups from the command-line with 'useradd' and 'groupadd' (not 'createuser' anymore), but the graphical utility is pretty fool-proof. Note that a user called 'mail' is there by default. I would create separate users for this system (e.g. 'tcmail' and 'tcserver'), rather than use names like 'httpd' that could by confused with built-in accounts later.
Static Web content hasn't been in /home/httpd for a long time. The correct location is now /var/www/html.
I can't help with Postgresql, but I do know that it has also changed a lot since RH 6.1, so I wouldn't trust that portion of the install notes either.