IE4plus = (document.all) ? true : false;
NS4 = (document.layers) ? true : false;
function clickIE(){ return false; }
function clickNS(e) { if (e.which==2 || e.which==3) { return false; } }
if (!IE4plus) {
   document.captureEvents(Event.MOUSEDOWN || Event.MOUSEUP);
   document.onmousedown=clickNS;
   document.onmouseup= clickNS;
   document.oncontextmenu=clickIE; // For NS 6+
} 
else 
{
   document.onmouseup= clickIE;
   document.oncontextmenu=clickIE;
}