function centerdiv(Xwidth,divid) { 

var centerX;
if( document.body ) {
centerX = document.body.clientWidth;
}
var leftOffset = (centerX - Xwidth) / 2;

var o=document.getElementById(divid);
var r=o.style;
r.position='absolute';
r.top = '50px';
r.left = leftOffset + 'px';
r.display = "block";
}