Help Reverse Engineer Auto resize Background Image (with Working Example)

https://www.amypink.com/

This guy has a working background auto-resize. I want to do the same thing, BAD!

Can anyone help me do this?? This is obviously not a real background image, but rather an image with a CSS ID and some other hijinks worked in.

I took a look at his stylesheet and it has this, but when I put it in to my code (and I don’t even know how to use the bodyDiv class) it puts the image ON TOP of the content.

He even got this code to work in IE6. I am impressed! Please help with this project:

/* BG-Image auf unterste Ebene anordnen */
#bgImg{ position: absolute;
top: 0;
left: 0;
border: 0;
z-index: 1;

min-height : 50%;
min-width : 50%;
margin : 0 auto;

}
/* Body-Dummy absolut ?ber BG-Image legen; Scrollbar bei Bedarf einblenden */
#bodyDiv{ position: absolute;
top: 0;
left: 0;
z-index: 2;
overflow: auto;
width: 100%;
height: 100%;
text-align: center;
vertical-align : middle;}