I think that you can just open the web.config file as XML and look to
"//system.web/compilation" node and then check it's debug attribute:

       Dim result As String
       Dim doc As XmlDocument = New XmlDocument
       doc.Load("C:\CDROM\wwwroot\OnLineTesting\web.config")
       Dim xPath As String = "//system.web/compilation"
       Dim node As XmlNode = doc.DocumentElement.SelectSingleNode(xPath)
       If Not node Is Nothing Then
           Dim attr As XmlAttribute = CType(node.Attributes("debug"),
XmlAttribute)
           If Not attr Is Nothing Then
               result = attr.Value
           End If
       End If

HTH