background image question; resize to screen?

Hi.
I’m in need of a bit of help.

Is there anyway to get background images to resize to different resolutions depending on who is viewing it?
The best example being; I have a monitor which is 1400×900 and the backgruond image fits the site perfectly, but I also want someone who has a monitor which is 1024×768.
IS this possible? I’ve looked round the internet and people have spoken about some custom java script, but it isn’t really much help to me.

Sorry for not explaining it very well as I can’t think how to describe it.

Any help would be fantastic.
Thank you.