function disableRightClick( evnt ) {
 if(navigator.appName.substring(0,9) == "Microsoft") {
  if ( event.button==2 ){
   alert("Copyright © 1999-2007, Luis Alvarado, All Rights Reserved.");
   return false;
  }
 } else if(navigator.appName.substring(0,8) == "Netscape"){
    if ( evnt.which==3 ){
     alert("Copyright © 1999-2007, Luis Alvarado All Rights Reserved.");
     return false;
    }
 }
}
if (document.layers) {
    document.captureEvents(Event.MOUSEDOWN)
}
document.onmousedown = disableRightClick;
<!--
bName = navigator.appName;
bVer = parseInt(navigator.appVersion);
    if ((bName == "Netscape" && bVer >= 3) || 
        (bName == "Microsoft Internet Explorer" && bVer >= 4)) br = "n3"; 
    else br = "n2";