MSXML2.ServerXMLHTTP.x.0

Function ProgIDInstalled(progID)
    On Error Resume Next
    Dim o : Set o = CreateObject(progID)
    ProgIDInstalled = Err.Number = 0
End Function

If ProgIDInstalled("MSXML2.DOMDocument.3.0") Then
    ' MSXML3 is present   '
End If

If ProgIDInstalled("MSXML2.DOMDocument.4.0") Then
    ' MSXML4 is present   '
End If

If ProgIDInstalled("MSXML2.DOMDocument.5.0") Then
    ' MSXML5 is present   '
End If

If ProgIDInstalled("MSXML2.DOMDocument.6.0") Then
    ' MSXML6 is present   '
End If

http://stackoverflow.com/questions/941725/msxml2-serverxmlhttp-4-0-source