如何获取Ajax div内容？

Dim objWshShell,IE,searchStr
Set objWshShell = Wscript.CreateObject("Wscript.Shell")
Set IE = CreateObject("InternetExplorer.Application")
With IE
  .Visible = true
  .Navigate "http://site"
  Do While .Busy
    WScript.Sleep 100
  Loop
.....
.....
End With

How to get contents for <div id="ajax_div"></div> because didn't show codes in page source.