function suckerfish(type, tag) {
   if(window.attachEvent) {
      window.attachEvent("onload", function() {
         var sf_els = document.getElementsByTagName(tag);
         type(sf_els);
      });
   }
}

sf_focus = function(sf_els) {
   for(var i=0; i<sf_els.length; i++) {
      sf_els[i].onfocus=function() {
         this.className+=" sffocus";
      }

      sf_els[i].onblur=function() {
         this.className=this.className.replace(new RegExp(" sffocus\\b"), "");
      }
   }
}

suckerfish(sf_focus, "INPUT");
suckerfish(sf_focus, "TEXTAREA");