Targetting elements via javascript... how?

Question

The following is code for a navigation menu where only one option appears lit at a time (based on code sent to me by the amazing Jon Fritz II).
CSS:
a#button0, a#button1 {
    display:block;
    float:left;
    width:55px;
    height:67px;
    margin:0;
a#button0.inactive
{ background:url(/carousel_home.png) -55 0 no-repeat }
a#button0.active
{ background:url(/carousel_home.png) 0 0 no-repeat }
a#button1.inactive
{ background:url(/carousel_vip.png) -55px 0 no-repeat }
a#button1.active
{ background:url(/carousel_vip.png) 0 0 no-repeat }
HTML:
<a href="#" onclick="changeClass(this)" class="inactive menu" id="button0"> </a>
<a href="#" onclick="changeClass(this)" class="inactive menu" id="button1"> </a>
JSCRIPT:
<script>
function changeClass(elClass) {
  var divsLength =  document.getElementsByClassName("menu").length;
  for (i = 0; i < divsLength; i++) {
    document.getElementsByClassName("menu")[i].className = "inactive menu";
  elClass.className = "active menu"; 
</script>
What this does is swap the class of a clicked button (in a menu) while reverting all the other buttons back to their original state, so only 1 button appears "lit" at a time. The A tags are used as block elements that simply shift the background image so as to produce a "lit" and "unlit" state.
My question is... via javascript (or anything else), is it possible to trigger class changes for the buttons from an area OUTSIDE the menu? In other words, can we make a text link on the page itself trigger which button in the menu to "light up". Something like <a href="javascript:slide('div1'); javascript:(go light up button1)">Example</a>
The reason is that this menu is not the ONLY way to get from one section to another. So if I click on a link in another DIV on the same page that takes me to another area, ideally, I'd like to see the button representing that area in the nav menu light up like it's been clicked on -- even if it hasn't. And of course, the other buttons would NOT be lit.
Thanks!

Answer 1

I hadn't even noticed you changed the name of the function from changeClass to setClass, which of course who immediately explain why it started working on those elements that were still calling changeClass... except that when I changed the individual calls to setClass, they still wouldn't work.
Was I supposed to leave the former changeClass function in the javascript? Is your setClass function supposed to be used in conjuction with the other one? Because I replaced one with the other, and ever since then, the new behavior works but the old one (clicking directly on the icon) does not.
Here is my menu :
<a href="javascript:slide('div-home')" onclick="setClass(this)" class="inactive menu" id="button0"> </a>
<a href="javascript:slide('div-vip1')" onclick="setClass(this)" class="inactive menu" id="button1"> </a>
<a href="javascript:slide('div-vip2')" onclick="setClass(this)" class="inactive menu" id="button2"> </a>
<a href="javascript:slide('div-vip4')" onclick="setClass(this)" class="inactive menu" id="button4"> </a>
<a href="javascript:slide('div-vip5')" onclick="setClass(this)" class="inactive menu" id="button5"> </a>
<a href="javascript:slide('div-done')" onclick="setClass(this)" class="inactive menu" id="button6"> </a>