I’m having a problem with my background image

On my pc, and on all the pcs in my house(3)using Firefox and IE my background appears like this:

https://img.photobucket.com/albums/v367/vgmaster937/websitephoto.jpg

Ive been on other people’s computers and my background image doesn’t always line up the way it is in that image above. Is there a way I can get the background image to line up with the main page no matter what size screen or if someone is using AOL or something?