How did they do this?

[gamerscalling]

http://www.thewreckers.com/site/index.html

I want to know how they did the image in the background in these.
I know how to put one in the background and have it tile and such.
But I really would like to know how they go about sizing it and controlling it's quality as it loads and so on. I think I want to do something like this on the site I am currently working on.

Thank you!