function alternate(id){ 
 if(document.getElementsByTagName){  
   var table = document.getElementById(id);   
   if (table != null)
   {
     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"; 
       }       
     }
   } 
 } 
}