[PHP] how to retrieve a dom from innerHTML......

[I am on the top of the world! Borlange University]

hello, i can obnot retrieve a select ject from div innerHTML.
what i want to do is that when a page is loaded, first selector,say #1,
would be shown in the first div by sending a request.then i choose one
option from #1, fire change event of #1, the second selector #2 will be
shown in div two, then choose option from #2 .............blabla..

but the problem is when selector #1 was loaded, the object #1 could not be
obtained.
codes:

window.addEvent('domready', function() {

 var option=1;

 var result = new Request({
  
url:'getInfo_gx.php'<https://mail.google.com/mail/html/compose/static_files/'getInfo_gx.php'>
,
  method:'get',
  onSuccess:function(response)
  {
   if(option==1) $('list_sch').innerHTML = response;         //response =
"<select id='sch_list><.......'";
   else if(option==2) $('list_gg').innerHTML = response;
   else $('list_gx').innerHTML = response;

  }
 });


result.send('type=1');    // page loaded,sending a request.


 $('list_sch').innerHTML = "<select id='sch_list'><option
value='123'>123312</option></select>";


 if($('sch_list'))             // heres the problem... object can not
be obtained.
 {
   $('sch_list').addEvent('change',function(){               // events
can not be  fired
   option=2;
   result.send('type=2'+'&sch='+$('sch_list').value.replace('+','%2B'));
  });
 }

});