How Do I Create A Scalable Background In Thesis

Hi guys,

I’m hoping someone can help me create a scalable background using Thesis.

The page that I’m working on is :
http://homerunseocom.netfirms.com/?page_id=91&preview=true

It looks great on a widescreen (1920×1200) monitor, but on anything smaller, the whole image is pushed to the right, so that the baseball image is in the center (or near to it), which I do not want….

Any help is appreciated in advance !