Pulling Data From Website In .NET And C#

I have written a web scraping program to go to a list of pages and write all the html to a file. The problem is that when I pull a block of text some of the characters get written as '�'. How do I pull those characters into my text file? Here is my code:

string baseUri = String.Format("http://www.rogersmushrooms.com/gallery/loadimage.asp?did={0}&blockName={1}", id.ToString(), name.Trim());

// our third request is for the actual webpage after the login.
HttpWebRequest request =
(HttpWebRequest)WebRequest.Create(baseUri);
request.Method = "GET";
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1)";
//get the response object, so that we may get the session cookie.
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
// and read the response
string page = reader.ReadToEnd();
StreamWriter SW;
string filename = string.Format("{0}.txt", id.ToString());
SW = File.AppendText("C:\Share\" + filename);
SW.Write(page);
reader.Close();
response.Close();