start script on load page (div)

I found this 404 error page, that displays some text when the page gets loaded.
The original page can be found here:
[url]http://80.60.218.3/oob.com/error_pages/404.html[/url]

I am trying to put this into my site, wich contains all content in a div block.
My question is, how do i get this script to start when the div block/page gets loaded?

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