servlets and jsp doubt

hi,
I have written a servlet

import music.business.User;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

import music.data.*;

public class RegisterUserServlet extends HttpServlet
{
    public void doGet(HttpServletRequest request,
                  HttpServletResponse response) throws IOException,
 
ServletException {
  doPost(request, response);
}

    public void doPost(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException, ServletException
    {
        HttpSession session = request.getSession();

        String firstName = request.getParameter("firstName");
        String lastName = request.getParameter("lastName");
        String emailAddress = request.getParameter("emailAddress");

        User user = new User();
        user.setFirstName(firstName);
        user.setLastName(lastName);
        user.setEmailAddress(emailAddress);
        try
        {
        if (UserDB.emailExists(emailAddress))
            UserDB.update(user);
        else
            UserDB.insert(user);
        } catch(Exception e) {}
        session.setAttribute("user", user);

        Cookie emailCookie = new Cookie("emailCookie", emailAddress);
        emailCookie.setMaxAge(60*60*24*365*2);
        emailCookie.setPath("/");
        response.addCookie(emailCookie);

        String url = "/catalog/writeDownload";
        RequestDispatcher dispatcher =
            getServletContext().getRequestDispatcher(url);
        dispatcher.forward(request, response);
    }

    }

my jsp code is calling this servlet

<jsp:include page="/includes/header.html" />
<jsp:include page="/includes/column_left_all.jsp" />

<!-- start the middle column -->

<td>

  <script language="JavaScript">
    function validate(form) {
        if (form.firstName.value=="") {
            alert("Please fill in your first name");
            form.firstName.focus();
        }
        else if (form.lastName.value=="") {
            alert("Please fill in your last name");
            form.lastName.focus();
        }
        else if (form.emailAddress.value=="") {
            alert("Please fill in your email address");
            form.emailAddress.focus();
        }
        else {
            form.submit();
        }
    }
  </script>

  <h1>Download registration</h1>

  <p>Before you can download and listen to these sound files,
  you must register with us by entering your name and email
  address below.</p>

  <!-- Import the core JSTL library -->
  <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

  <!-- Use the JSTL url tag to encode the URL -->
  <form action="<c:url value='/catalog/registerUser'/>"
        method="post">
    <table cellpadding="5" border="0">
      <tr>
        <td align="right"><p>First name:</td>
        <td><input type="text" name="firstName"></td>
      </tr>
      <tr>
        <td align="right"><p>Last name:</td>
        <td><input type="text" name="lastName"></td>
      </tr>
      <tr>
        <td align="right"><p>Email address:</td>
        <td><input type="text" name="emailAddress"></td>
      </tr>
      <tr>
        <td></td>
        <td><input type="button" value="Submit"
                   onClick="validate(this.form)"></td>
      </tr>
    </table>
  </form>

</td>

<!-- end the middle column -->

<jsp:include page="/includes/column_right_buttons.jsp" />
<jsp:include page="/includes/footer.jsp" />

when i run my servlet,browser display this message-

HTTP Status 405 - HTTP method GET is not supported by this URL

i have given proper url to this servlet through web.xml also.

kindly help me to provide solution for this problem.
Thank you.