The drupal forms API is new to me .... I have not tried to use it before. Searching on the drupal site I found..

Main section of the developing for drupal section for Forms API I need to read it a few times.. and the world famous Forms API Reference

Solution for a custom contact form with file attachment I just copied the code into a "new page" (input format=PHP) and it worked... before you submit you should change the email it goes to..(I didn't and got an auto response from Germany...)

Small form sample... this seems to help explain what is not explained in the next link... where you think it should be... I am going to try it out -- yes the multiply 2 numbers module works great.. this is a very interesting discussion.

The Forms API Quickstart Guide tells you info but the example form didn't work for me... maybe I will understand why if I study hard.

Of course there is a pretty good module out there to create forms... it worked as expected and even sends emails and does some statistics it is called "webform" what else would it be...

Multipage forms with the Forms API has code for a "working" example ... I have yet to try that.

How to use tables in drupal Form API

How to use dates in forms

how to validate items on a form

Notice of version 2 -- drupal - it changes fast Forms API reaches version 2.0 so I guess it will make the code freeze..