Custom 404 Page

I know how to make a custom 404 page in WordPress, I am just having trouble doing it in Directory Press. The 404.php file I find is just oriented to an admin. When it is not an admin, the only thing that comes up is a title: “404 Error – File Not Found”. I’ve looked through the instructions and tutorials and find no reference to a custom 404 page.

1. Where would I put text/code that anyone else would see?
2. Can I substitute a 404 page of my own and would it work?
3. Am I just missing where to do this in the backend, i.e. where to put my custom text or what page to designate as my 404 page?

Thanks in advance,
Julie