using vb.net to post XML

I have this SOAP document that i'm trying to post:

Code:

---

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<soap:Body>
<FahrenheitToCelsius xmlns="http://tempuri.org/">
<Fahrenheit>10</Fahrenheit>
</FahrenheitToCelsius>
</soap:Body>
</soap:Envelope>

---

and here is the code:

VB Code:

url2= "http://www.w3schools.com/webservices/tempconvert.asmx/FahrenheiToCelsius"
        httpRequest = CreateObject("Microsoft.XMLHTTP")
        httpRequest.open("post", url2, False)
        httpRequest.send(CType(httpReq, Object))
        Dim resp As String = httpRequest.responseText

httpReq is the SOAP document. At the end of the code, i get a "Request format is invalid." message. Any idea why?