If you need to set the user agent, you can cast the WebRequest to HttpWebRequest and set the UserAgent property. Here is an example:
Dim wr As HttpWebRequest = DirectCast(WebRequest.Create(strURI), HttpWebRequest)
wr.UserAgent = "Mozilla/5.0....."
As for the encoding, you can cast the response to HttpWebResponse and get the Encoding property from there. Here is an example:
Dim response As HttpWebResponse = DirectCast(wr.GetResponse(), HttpWebResponse)
Dim sr As New StreamReader(response.GetResponseStream(), response.Encoding)
Dim responseText As String = sr.ReadToEnd()
Note that the response's encoding might not be the same as the request's encoding, so you might want to check for that.