window.onload = resizeDiv;
window.onresize = resizeDiv;

function resizeDiv()
{
	//settings
	var larghezzaMin = 450; //larghezza del div per uno scherzo 1024x768
	var classDiv = 'resizeableDiv';
	
	var myDiv = document.getElementById('resizeableDiv');
	
	var viewportwidth;
	var viewportheight;
	 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
	 }

	if(viewportwidth < 1025)
	{
		myDiv.style.width = larghezzaMin + 'px';
	}
	else
	{
		myDiv.style.width = '35%';
	}
}