Home Page Custom Background Layout

Home Page custom background layout..


my homepage:

JetGaming - Gaming Mayhem


Im gettin bored of the gradient and like most gaming sites you can switch between like say game background, how exactly would i do that? If someone could help me with or if you need the CSS to see then view source and download or view it, The support of the template said you would create a large background with an image of your choice then leave a large transparent area in the middile for the actual site and use CSS to position it (absolute), and i have no idea as i dont know CSS..

Heres a demo of what i mean:

IGN.com: Video Games, Cheats, Movies and More

IGN regularly change their background depending on a game.