How to use HttpWebRequest to send POST request to another web server?

How to use HttpWebRequest to send POST request to another web server?

要提交象以下格式的表单：
<form name="_xclick" target="paypal"
action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="business" value="me@mybiz.com">
<input type="hidden" name="item_name" value="HTML book">
<input type="hidden" name="amount" value="24.99">
<input type="image" src="http://www.paypal.com/images/sc-but-01.gif"
border="0" name="submit" alt="Make payments with PayPal!">
<input type="hidden" name="add" value="1">
</form>

POST方法写法如下：
private void OnPostInfoClick(object sender, System.EventArgs e)
{
string strId = UserId_TextBox.Text;
string strName = Name_TextBox.Text;

ASCIIEncoding encoding=new ASCIIEncoding();
string postData="userid="+strId;
postData += ("&username="+strName);
byte[]  data = encoding.GetBytes(postData);

// Prepare web request...
HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create("http://localhost/MyIdentity/Default.aspx");
myRequest.Method = "POST";
myRequest.ContentType="application/x-www-form-urlencoded";
myRequest.ContentLength = data.Length;
Stream newStream=myRequest.GetRequestStream();
// Send the data.
newStream.Write(data,0,data.Length);
newStream.Close();
//读取response
res = (HttpWebResponse)req.GetResponse();
Stream ReceiveStream = res.GetResponseStream();
Encoding encode = System.Text.Encoding.GetEncoding(utf-8);
StreamReader sr = new StreamReader( ReceiveStream, encode );
Char[] read = new Char[256];
int count = sr.Read( read, 0, 256 );
while (count > 0)
{
String str = new String(read, 0, count);
strResult = str;
count = sr.Read(read, 0, 256);
}

}