access data of the second layer in a form (Netscape)

Hi,

I would appreciate some help for the next question:

I have a form with two layers.

In IE there is not problem but in Netscape I can't access to the second layer.
(In JavaScript I have a function for refresh the second layer):

function load( layer, src ) {
     var object;
     if ( NN4 ) {
          object = eval( 'document.layers[\''+ layer +'\']');
          object.src = src;
     }
     else if ( IE4 ) {
          object = eval( 'document.frames["' + layer + '"].document' );
          object.location = src;
     }
}

IE:
<FORM>....
<Frame name="a">....
</Frame>
<Frame name"b">....
</FRAME>

Netscape:
<FORM>...
<Layer name="a">.....
</Layer>
<Layer name="b">....
</Layer>


How can I access to the second layer?
I have readen that in Netscape only is possible have one layer per form!!!!

Regards,