xmlhttp方法抓取下一页问题

http://www.hyey/Drug/DrugList.aspx?fl=2
我想抓取这个页面的下一页，他采用了__VIEWSTATE这个参数限制了，看谁有办法帮我解决下，下边是代码，post的参数都取到了，看看是不是xmlHttp.setRequestHeader这个头参数哪里不对

 postdate="__VIEWSTATE="&VIEWSTATE&"&__EVENTVALIDATION="&EVENTVALIDATION&"&txtPageSizeV=2"
postCode=PostHttpPage(ListUrl,ListUrl,postdate)

Function PostHttpPage(RefererUrl,PostUrl,PostData) 
    Dim xmlHttp 
    Dim RetStr      
    Set xmlHttp = CreateObject("Msxml2.XMLHTTP")  
    xmlHttp.Open "POST", PostUrl, False
    XmlHTTP.setRequestHeader "Content-Length",Len(PostData) 
    xmlHttp.setRequestHeader "Content-Type", "text/html,application/xhtml+xml,application/xml"
    xmlHttp.setRequestHeader "Connection", "Keep-Alive"
xmlhttp.setRequestHeader "Cache-Control", "no-cache"
    xmlHttp.setRequestHeader "Referer", RefererUrl
    xmlHttp.Send PostData 
    If Err.Number <> 0 Then 
        Set xmlHttp=Nothing
        PostHttpPage = "$False$"
        Exit Function
    End If
    PostHttpPage=bytesToBSTR(xmlHttp.responseBody,"GB2312")
    Set xmlHttp = nothing
End Function