var nav = (document.layers) ? true : false;
var iex = (document.all) ? true : false;
<!-- Don't let the next 2 statements wrap... They must be one line each, otherwise they will not run, and you will get javascript errors --> 
if(iex) document.write('<div style="position:absolute; ID:banner; left:498px; top:0; width:393px; height:115px; visibility:visible; z-index:100" ><a href="" onClick="clickLink(); return false;" onMouseOver="descript(); return true;"onmouseout="nothing()"><img src="head_foot_files/banner1.jpg" border=0 name="banner" width="520" height="115"></a></div>')
if(nav) document.write('<layer left="332" top="13" width="393" height="115" z-index="100" visibility="show" ID="banner" ><a href="" onClick="clickLink(); return false;" onMouseOver="descript(); return true;" onmouseout="nothing()"><img src="head_foot_files/banner1.jpg" border=0 name="banner" width="520" height="115"></a></layer>')