invalid soap request...help

why doesn't this soap request work?

Code:

---

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <FahrenheitToCelsius xmlns="http://tempuri.org/">
      <Fahrenheit>10</Fahrenheit>
    </FahrenheitToCelsius>
  </soap:Body>
</soap:Envelope>

---

I'm sending this way:

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))  'httpReq is the SOAP request above
        Dim resp As String = httpRequest.responseText

after it runs thru the code, i get a "The request format is invalid;." Anyone know how to make it work?