[jQuery] Menu / prev()

[HerrJuergen]

Hi,

i'm trying to create a Tree Menu as follows

<ul>
   <li class="nav_main_inactive">Category A</li>
   <li class="nav_sub_inactive">Category A, Subcategory A</li>
   <li class="nav_sub_inactive">Category A, Subcategory B</li>
   <li class="nav_sub_inactive">Category A, Subcategory C</li>
   <li class="nav_main_inactive">Category A</li>
   <li class="nav_sub_inactive">Category A, Subcategory A</li>
   <li class="nav_sub_inactive">Category A, Subcategory B</li>
   <li class="nav_sub_inactive">Category A, Subcategory C</li>
</ul>

all of the nav points are always visible

if i click a "sub_nav_inactive" the class of it changes to
"sub_nav_active" to highlight it - that works great
but the parent (yeah i know it isn't) "main_nav_inactive" class should
be changed to "main_nav_active"

so the main category should be highlighted as well as the selected
subcategory of it

if i use

$(".nav_sub_inactive").bind("click", function(){

.... change the class etc

     $(this).prev("li.nav_main_inactive").toggleClass
("nav_main_active");

     // that doesnt work, except when its the very prev of it :(
});

whats wrong?????

please please help me

thanks in advance