The quickest-and-dirtiest way I can think of off the top of my head is to wrap your entire page in a div with a "visibility: hidden" style property. Then, once the page is loaded (e.g. use window.onload to fire a JS function when this happens), change that div's visibility value to "visible".
While the page is loading, you could have a div display that says "Loading..." or whatever. Obviously, when you toggle the other div's visibility, you would set this 'loading' div to "display: none".