I always link in all my js in the head of the document so it loads before the body (I think thats correct anyway) which might help. Your using
so this can also be put in the head as the script will only run when the document is ready (and the target div has been created).
At the moment your page is going draw all this, then load in jquery etc, then run the script. Stick it in the head and jquery etc should be loaded in time to stop the images displaying.
If that fails you could just a .hide() in the js before and then a .show() after the slider function or add a display: none in the css and toggle it to show with js.
Couple of ideas there that should work, somebody else might have a more elegant solution though!
ps check your site in IE6 few layout issues (Although im guessing your working on it!)
EDIT: yeh actually setting a height and adding overflow:hidden on the container should do it :-s
EDIT EDIT: Ah yeh looks like js is adding the inline overflow:hidden / height. try sticking it in your css as a defined style