OR, you could define the 404 Error page in a .htacces file lke this:
code:
ErrorDocument 404 /error404.htm
And then when a page doesn't excist it will redirect to error404.htm in the directory where you have the .htacces file
Example for my website:
http://www.tsdme.nl/bullshitpagethatisntthere.htm
EDIT: I didn't read the website you provided correctly, anywaay, this is how to redirect to a 404