be able to throw something together later that displays an image while the page loads. Of course if you use an image, then the image must load first, which could defeat the purpose. You could over come this by pre loading the image you use in the head of the main page containing the iframe.
I'll look into it a bit later on. In the meantime, there are some page effects here you might want to take a look at and give one a try: http://www.dynamicdrive.com/dynamicindex3/document2.htm
By increasing the duration, you might be able to achieve a suitable effect