if(document.getElementsByTagName){
   var table = document.getElementsByTagName('table');
   for(j = 0; j < table.length; j++){
     var rows = table[j].getElementsByTagName("tr");
     for(i = 0; i < rows.length; i++){
       if(i % 2 == 0){
         rows[i].className = "even";
       }else{
         rows[i].className = "odd";
       }
     }
   }
 }