var sidebarWidth = 190;
var mainWidth = 700;
var minMargin = 10;
var divId = "page-wrap";

function fixMargin() {
	var viewportwidth;
	var viewportheight;
	// the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
	if (typeof window.innerWidth != 'undefined')
	{
		viewportwidth = window.innerWidth,
		viewportheight = window.innerHeight
	}
	// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
	else if (typeof document.documentElement != 'undefined'
		 && typeof document.documentElement.clientWidth !=
		 'undefined' && document.documentElement.clientWidth != 0)
	{
		 viewportwidth = document.documentElement.clientWidth,
		 viewportheight = document.documentElement.clientHeight
	}
	// older versions of IE
	else
	{
		 viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
		 viewportheight = document.getElementsByTagName('body')[0].clientHeight
	}
	var offset = (viewportwidth - mainWidth) / 2;
	var leftMargin = offset - sidebarWidth;
	if(leftMargin < minMargin) leftMargin = minMargin;

	document.getElementById(divId).style.marginLeft = leftMargin + "px";
}

fixMargin();