I don't know if this will help you, but I had a similar problem where I 
had an embedded DIV inside two layers of Tables (don't ask), where I was 
trying to get the DIV to become hidden and visible by an action somewhere 
else.  I found that if I define the ID of each DIV in a style sheet that I 
can then access them through javascript. Like so:

..<style>
..<!--
..#test  {position: relative;}
..#test1 {position: relative;}
..-->
..</style>

It seems that NN4 could not find the objects until I did this then it was 
just a matter of using something as simple as:

..var thisLayer=eval("document."+objToBeTested);

and I had access to the object's properties

I hope that helps,

Karry