[activate lightbox popup via javascript function]

How?

pretty simple question for anyone familiar with LB I'm sure, please help!

I need to do something like this (and this is what I've been trying):
Code JavaScript:
myLightbox.start('file:///C:/Users/Leoj/Desktop/lb/images/loading_your_images_now.jpg'); return false;
//preload a bunch of images
myLightbox.end();