layer problems w/ javascript

i have some <div> layers in a web page, and an image with the attribute
onMouseover="popUp('thePopup');"
where thePopup is the id of one of my layers. here is the popUp function:
function popUp(layerName)
{
if(document.layers)
{ document.layers[layerName].visibility="show"; }

else
{ document.all[layerName].style.visibility="visible"; }

}

this works in IE but not in netscape. what am i doing wrong?

i have a similar problem. i call a function inside a div tag that forwards to a url on a change in a select pulldown menu. it won't work in netscape unless i get rid of the style attribute in the div tag...

what the %$#@...