Eh, wow, sorry about that, I misread your first post.
The only thing I can think of, is to wrap your entire layout, that means placing the start tag right
after your body tag, and the end tag right before
your closing body tag, in a <div>, and do something like this:
<div id="preload" style="visiblity:hidden;">
all of your content, ect., ect...
Although, this will mean that your whole site won't be visible to those who don't have JS enabled...
Eh, sorry, I'm a bit lost, but do you want your entire page to load like this, or just one/a few images?