I need to unset terms from the drop down I'm writing a module to unset taxonomy terms using D6 hook_form_alter(). The object is to only present the current user terms which they have created themselves.

The trouble is that I don't know which variables to alter. I'm thinking it should be something like $form['taxonomy']['2']['#options'], but I cannot see a path in a DSM print_r($form).

I have gone through hierarchical_select.module again and again, but can't work out whether I need to be amending the results of $storage, $elements, #names, $hsid or any of the other variables; I am not sure about which hook to use too.

I just need to know how to apply the results of this db_query() in my custom module code which you can see on http://pastebin.com/RbwKB0rt.

Can anybody please help?
I think I need more information.

In general, I believe you set the #default_value on your dependent form element to be the parent element, and also set the #ajax callback and wrapper on the parent. Check out the Ajax example and the form API reference.