create http post using webclient or web request

Hi
I would like to create http post request the code below is html version but I want to do it using class library (web client or Webrequest etc)
  <form action="https://demo.paypal.com/us/home" method="post">         product id: <input type="text" id="product_id" name="product_id" value="abc" />         <br />         return url: <input type="url" id="return_url" name="return_url" value="http://www.MYWEBSITE.COM" /         <input type="submit" />     </form>
I would like to know how can I do this using asp.net button click and call cl ...