Theming user-edit form drupal 6 After installing tons of modules like guestbook, subscriptions etc. It also added tons of settings on user/$uid/edit page. How can I disable or rearrange them?

I guess theme_fieldset() would help me, but I have no idea how to use it correctly. And where to print_r($form) and in which template?
devel themer will help you understand what you can over ride and what variables are available. 

hook_form_alter() can be used to trim fields that you don't want and to re order the form, put things into groups etc.