Here we go!
The following is an example use of the .htaccess ErrorDocument file to send '404' Page Not Found Errors to your own custom error page.
You will see that it is so simple that it's almost silly...
Simply make a text file in NOTEPAD (for a Windows based system) with the following:
ErrorDocument 404
http://www.yourdomain.com/your-404-page.html
Then save the file as ' .htaccess '
Then FTP it to your root web sites directory (the directory that the FTP puts you in when you first log-in).
Thats it !