var viewportwidth;
var viewportheight;
if (typeof window.innerWidth != 'undefined')
{
	viewportwidth = window.innerWidth,
	viewportheight = window.innerHeight
}
// IE6
else if (typeof document.documentElement != 'undefined' && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0)
{
	viewportwidth = document.documentElement.clientWidth,
	viewportheight = document.documentElement.clientHeight
}
// IE6-
else
{
	viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
	viewportheight = document.getElementsByTagName('body')[0].clientHeight
}

if(viewportwidth < 900 || viewportheight < 600) {
	document.write('<style type="text/css">.centre {width: 930px;height: 590px;position: relative;margin: 20px auto;top: 0;left: 0;}</style>');
}