CSS ~ set height 100%

html {
height: 100%;
}

body {
margin: 0;
padding: 0;
height: 100%;
}

#content {
background: #EEE;
border-left: 1px solid #000;
border-right: 1px solid #000;
padding: 0 20px 0 20px;
margin: auto;
font: 1.5em arial, verdana, sans-serif;
width: 960px;
min-height: 100%;
}


reference
http://www.tutwow.com/htmlcss/quick-tip-css-100-height/