function alternate(id){ 
 if(document.getElementsByTagName){  
   var table = document.getElementById(id);   
   var rows = table.getElementsByTagName("tr");   
   for(i = 0; i < rows.length; i++){           
 //manipulate rows 
     if(i % 2 == 0){ 
       rows[i].className = "even"; 
     }else{ 
       rows[i].className = "odd"; 
     }       
   } 
 } 
}