getElementById in loop

Hi,

I'm using a function, where I loop all form elements with the purpose to hide them if a menu-item (layer) is being shown above it.

Looping the form elements works in netscape and IE, but in netscape the calls elemTop, getPageLeft, elemRight, elemBottom don't give me any result.

How can I make the script below work in netscape?

Thanks,
Floris.

function toggleSelectElements(layer, mode) {
  var e, f, elem, elemTop, elemLeft, elemRight, elemBottom;
 
  // Loop through all forms in document
  for (f = 0; f < window.document.forms.length; f++) {
     for (e = 0; e < window.document.forms[f].elements.length; e++) {
       if ( window.document.forms[f].elements[e].type == "select-multiple" ||
            window.document.forms[f].elements[e].type == "select-one" ) {
          elem = window.document.forms[f].elements[e];
          elemTop = getPageTop(elem);
          elemLeft = getPageLeft(elem);
        elemRight = elemLeft + elem.clientWidth ;
        elemBottom = elemTop + elem.clientHeight + 1;          
          // Test for overlap.
          if ( layer.left <= elemRight && layer.right >= elemLeft && layer.bottom >= elemTop ) {          
            if ( mode == 0 ) {            
                 if (isMinNS4) {
                    forms[f].elements[e].visibility="hide";
                    window.document.forms[f].getElementById("X3").visibility="hide";
                   
                    }
               else {
                      window.document.forms[f].elements[e].style.visibility="hidden";                    
                    }            
            } else {
                 if (isMinNS4) {
                     window.document.forms[f].elements[e].visibility="show";
                    }
               else {
                    window.document.forms[f].elements[e].style.visibility="visible";
                    }
            }
         }
       }
       }
  }
}