header >
301

301 Moved Permanently

Response.Status="301 Moved Permanently"

you may set up a default error page which content 
the 301 permanent redirect method

Response.AddHeader "Location", URI path

basic 301 can be a way to avoid  404 error message page appear

301 Redirect 主要目的为
永久性重新寻址
改变网址而不会出现「404 找不到网页」将(错误讯息页)设定Response.AddHeader

ASP

<%@ Language=VBScript %>
<%
Response.Status="301 Moved Permanently"
Response.AddHeader "Location", "http://another_site_page"
%>
----------------------------------------

ASPX
<script runat="server">
private void Page_Load(object sender, System.EventArgs e)
{
Response.Status = "301 Moved Permanently";
Response.AddHeader("Location","http://another_site_page");
}
</script>

Note: If your 301 is

http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

http://en.wikipedia.org/wiki/404_error