in reply to Send a Standard looking 404 error to unwanted vistors

There is no such thing as the normal 404 error page for a particular browser. The browser is displaying what the webserver is sending to it. Create a nice informational 404 page, telling the user to go elsewhere or get lost or something, and have the script send it to the user.

Here's a whole site dedicated to creating spiffy looking 404 pages: