How to make my website fit any screen size?

I designed my site within photoshop then used the slice tool and saved for web, I have tried. ` body {
padding: 0; margin: 0; }

div{
width: 100%;
height: 100%;
min-width: 1000px;
min-height: 1000px;
margin: 0 auto;
}

` in css with no luck. any ideas?