var min_height = 550; 
var idContent = 'content_1';
function checkMinHeight()
{
    var h = document.body.offsetHeight;
    var f = document.getElementById(idContent);
    if (h < min_height) { // the movie is taller than the window - don't try to center it vertically
        f.style.marginTop = '0px';
        f.style.top = '0%';
    } else {
        f.style.marginTop = '-'+(min_height/2)+'px';
        f.style.top = '50%';
    }
}
window.onresize = checkMinHeight;
window.onload = checkMinHeight;