Need Preloader where image "fills up"

I’m trying to create a preloader similar to http://www.oco.com/home/ where you have a hollow image created in flash and as the page content loads the image fills up at the rate its loading. I’d like to know how to create one with and without the percentage figure.

I tried modifying a percentage bar preloader but this gave me the wrong effect.

Anyone help?

Beamond
http://www.beamondcreative.com