PayPal PDT integration ASP.NET

Hi,
I'm going round in circles trying to integrate PayPal with my C# code. All I want to do is send the value of the shopping cart, e.g. £25.99 to paypal, have the client pay then send a response to PDT and update my database with SUCCESS, or FAIL response and return to my site.

I've set up Website Payments Standard code to send the form to paypal but nothing seems to be coming back to the PDT page in sandbox. There is so much documentation on the PayPal website that it I'm not sure where to look.

Does someone have some example code or know of a tutorial to get this done? It only needs to be really simple!

The code I tried to use is below, but I'm unsure where to go from here?

String strTransactionID = Request.QueryString["tx"].ToString();
    string sOut = "";
    string MyIDToken = "MyIdentityToken";
    string transactionID = Request.QueryString["tx"].ToString();
    string sCmd = "_notify-synch";
    string serverURL = "https: //www. paypal. com/cgi-bin/webscr";
    try
    {
        string strFormValues = Request.Form.ToString();
        string strPassValue;
        string strResponse;
        // Create the request back
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(serverURL);
        // Set values for the request back
        req.Method = "POST";
        req.ContentType = "application/x-www-form-urlencoded";
        //Append the transaction ID, ID Token, and command
        //to the form
        strPassValue = strFormValues + "&cmd = _notify-synch&at = " + MyIDToken + "&tx = " + transactionID;
        req.ContentLength = strPassValue.Length;
        // Write the request back IPN strings
        StreamWriter stOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
        stOut.Write(strPassValue);
        stOut.Close();
        // Do the request to PayPal and get the response
        StreamReader stIn = new StreamReader(req.GetResponse().GetResponseStream());
        strResponse = stIn.ReadToEnd();
        stIn.Close();
        sOut = Server.UrlDecode(strResponse);
    }
    catch (Exception x)
    {
    }

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Thanks,
NL