How to set the selected option for a combo box?

<div>         <label for="category" class="label_left">Kategorie</label>           <% @selected_category =            Category.find(:first, :select => "name, id", :conditions => ["id = ?", params['category_id']]) %>          <% @all_categories = Category.find(:all, :order => 'id').collect {|c| ([c.name, c.id])} %>          <select name='edition[category_id]' id='category' class='fieldStyle' tabindex='3'>         <%= options_for_select(@all_categories, @selected_category.name) %>      </select>   </div>