Creation of "404 Page Not Found" page

So I tried a random thing inside my forum:
http://www.mewtwoproject.net/rnrlkjndfkjfna

I want to create a 404, page not found error, how can I do that? Probably I will need a javascript or HTML page right?

UP

up

http://www.avacweb.com/t1254-replicating-a-custom-404-page and everything else you can find on avacweb

What is the link that that you want to have the 404?

I don't know things like this make no sense to me, what is the purpose of doing this?
if you want your forum to be closed then put it in construction or holiday mode.

Yes see you have to create a "fake" 404 as the 404 error and other errors are all done in the htaccess file which is simple labeled .htaccess and that can not be edited by anyone except for forumotion. It would be nice for us to be able to edit these within our admin panel but until then sorry. If you go to the link for avacweb I am also over there, and if you need anymore support on the custom 404 link we can provide more support. 

  If you'd rather not follow through the link you can give a comment back here and I can come up with a simple code for you though it being simple to me, it may be a little tricky for you.