Module development and code questions

Hi,
I want users to have a select list in which they can add a new value if it is not already there. For profiles this is done in the profile.module, but what about the rest of the system? Where is the input type/validation etc handled globally?

I'm trying to alter the Drupal contact form. I've changed some info, and removed the subject box.

function phptemplate_contact_mail_page($form) {

$form['contact_information']['#value'] = 'My fancy new message.';
#unset($form['subject']);

$output = drupal_render($form);
return $output;

}

The trouble is, I get an error that there is no subject, when the form is validated. How can I override this validation for the $form['subject'] ?

Hi,
I was hoping to use Drupal to have hierarchical user data, so that it can have other nodes associated to it. Is it possible to do this in Drupal?

e.g A user creates node_A, and then creates node_B1, node_B2 which are associated with node_A. Also, node_A has limits on what types of nodes can be attached to it, and how many of each.

Is this going to be really hard in Drupal? Drupal seems to be completely flat. Does anyone know of any examples of node types that have sub nodes and restricted sub node specifactions (both type and number)

I would like my user could visit a page and could create content direct in this page.

Example I create Menu
-Supliers
with sub-menus
--Doors
--Window
--Concrete

Hi, I wanted to install drupal vB but now I got an error after I went to admin -> settings -> drupal vB

It says:

I have a long list node display in bookpage and i want to use pager to seperate it in some page. How can i do that? anybody help me please?
Many thanks