function alternate(id){
if(document.getElementsByTagName){
if(document.getElementById(id) != null){ // make sure the id exists
   var table = document.getElementById(id);
   var rows = table.getElementsByTagName("tr");
   for(i = 1; i < rows.length; i++){     // start at i=1 so that you skip the header row
    //manipulate rows
    if(i % 2 == 0){
     rows[i].className = "even";
    }else{
     rows[i].className = "odd";
    }
   }
  }
 }
}