change template

Hello all,

I want to add something to my variations for the shop.
Now i have the categories template, but how do i add for example a combo box to it ?

<?php

class wpec_dot {

	function __construct() {
		add_action ( 'init', array ( &$this, 'register__taxonomy' ) );
	}

	function register__taxonomy() {

		$labels = Array (
			'name' => _x( 'Variations Extra', 'taxonomy general name', 'wpec_spo' ),
			'singular_name' => _x( 'Extra Variation', 'taxonomy singular name', 'wpec_spo' ),
			'search_items' => __( 'Search Variations Extra', 'wpec_spo' ),
			'all_items' => __( 'All Variations Extra' , 'wpec_spo'),
			'edit_item' => __( 'Edit Extra Variation', 'wpec_spo' ),
			'update_item' => __( 'Update Extra Variation', 'wpec_spo' ),
			'add_new_item' => __( 'Add new Extra Variation', 'wpec_spo' ),
			'new_item_name' => __( 'New Extra Variation Name', 'wpec_spo' )
		);

		register_taxonomy( 'wpec_', 'wpsc-product', array(
			'hierarchical' => true,
			'labels' => $labels,
			'rewrite' => false,
			'show_tagcloud' => false
			)
		);
	}

}

$wpec_dot_s_common = new wpec_dot();

?>

so i have changed the names that where already present, but how do I add new stuff to the page ?