Customize Admin Interface

Hi,

I would like to add a pic to all my categories.

I have no idea of where to start from. I tried adding code to my funcions.php file in the themes folder but I don’t know how to proceed with it. As:

add_action('edit_category_form', 'update_photo_for_cat');

add_action('add_category_form', 'add_photo_for_cat');

function add_photo_for_cat()
 {
	 //for the present category we need to display a text field where the user can copy paste a pic address
	 	  echo 'Image Path: ';
	 	  echo '<input type="text"></input>';

 }

Where will the form fields come in and how?