function phover(){
  if (!document.getElementById) return

  var p = document.getElementsByTagName('p');
  for(var i = 0; i < p.length; i++){
   p[i].onmouseover = function(){
    this.className = 'hover';
   }
   p[i].onmouseout  = function(){
    this.className = '';
   }
  }
}
window.onload = phover;