Variable width templates

I would like to be able to change the fix width template I am using to a variable width so it fills up all of my 1280 x 1024 screen, instead of jsut 770 pixels in the middle. Then of course, I want it to resize automatically down to fix those who use lower resolutions. I know it’s probably fairly easy to do, but I don’t know how!

Any pointers gratefully received..
I’ve jsut started using WordPress, so thought this would be a good time to tinker about with it