The Twitter API is really basic and effective. To accomplish what you're looking for all you'd have to do is add the following function and call it from the Coupon logic:
HTML Code:
public static void Twit(string StatusUpdate)
{
string URL = "http://twitter.com/statuses/update.xml?status={0}";
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
string.Format(
URL,
HttpUtility.UrlEncode(StatusUpdate))
);
request.Method = "POST";
//This should be your twitter user ID and password
request.Credentials = new System.Net.NetworkCredential(UserName, Password);
request.ContentType = "application/x-www-form-urlencoded";
request.ServicePoint.Expect100Continue = true;
//Called to fire the request
request.GetResponse().GetResponseStream();
}