// JavaScript Document
//Ancho y alto de la página
function Viewport(){ this.windowX = (document.documentElement && document.documentElement.clientWidth) || window.innerWidth || self.innerWidth || document.body.clientWidth; this.windowY = (document.documentElement && document.documentElement.clientHeight) || window.innerHeight || self.innerHeight || document.body.clientHeight; this.scrollX = (document.documentElement && document.documentElement.scrollLeft) || window.pageXOffset || self.pageXOffset || document.body.scrollLeft; this.scrollY = (document.documentElement && document.documentElement.scrollTop) || window.pageYOffset || self.pageYOffset || document.body.scrollTop; this.pageX = (document.documentElement && document.documentElement.scrollWidth) ? document.documentElement.scrollWidth : (document.body.scrollWidth > document.body.offsetWidth) ? document.body.scrollWidth : document.body.offsetWidth; this.pageY = (document.documentElement && document.documentElement.scrollHeight) ? document.documentElement.scrollHeight : (document.body.scrollHeight > document.body.offsetHeight) ? document.body.scrollHeight : document.body.offsetHeight;
}

<!-- inicio
var IE = document.all?true:false
if (!IE) document.captureEvents(Event.MOUSEMOVE)

document.onmousemove = posicRatonXY;

var posicX = 0
var posicY = 0

function posicRatonXY(e)
{
	if (IE)
	{ 
		posicX = event.clientX + document.body.scrollLeft;
		posicY = event.clientY + document.body.scrollTop;
	}	else { 
		posicX = e.pageX; posicY = e.pageY;
	}
	if (posicX < 0) {posicX = 0};
	if (posicY < 0) {posicY = 0};
	
	if (mov == 1)
	{
		var nub = document.getElementById("nube");
		
		var scrl = new Viewport();
		if (navigator.appName.indexOf("Microsoft") != -1)
			nub.style.top = (parseFloat(posicY) - 100 + scrl.scrollY) + "px";
		if (navigator.appName.indexOf("Netscape") != -1)
			nub.style.top = (parseFloat(posicY) - 100) + "px";
		
		if (document.getElementById('imgdetalle'))
			var imag = document.getElementById('imgdetalle');

		if ((parseFloat(posicX) + 20 + parseFloat(imag.width)) < scrl.windowX)
		{
			nub.style.left = (parseFloat(posicX) + 20) + "px";
		} else {
			nub.style.left = (parseFloat(posicX) - 20 - parseFloat(imag.width)) + "px"
		}
	}
	return true 
}
// final -->
var tout;
var mov;
function mostrar(img)
{
	mov = 1;
	var nub = document.getElementById('nube');

	var scrl = new Viewport();
	if (navigator.appName.indexOf("Microsoft") != -1)
		nub.style.top = (parseFloat(posicY) - 100 + scrl.scrollY) + "px";
	if (navigator.appName.indexOf("Netscape") != -1)
		nub.style.top = (parseFloat(posicY) - 100) + "px";
		
	if (document.getElementById('imgdetalle'))
		var imag = document.getElementById('imgdetalle');

	if ((parseFloat(posicX) + 20 + parseFloat(imag.width)) < scrl.windowX)
	{
		nub.style.left = (parseFloat(posicX) + 20) + "px";
	} else {
		nub.style.left = (parseFloat(posicX) - 20 - parseFloat(imag.width)) + "px"
	}
	nub.innerHTML = "<img id='imgdetalle' src='"+img+"' border='0'>";
	nub.style.visibility = 'visible';
}
function ocultar()
{
	nub = document.getElementById("nube");
	nub.style.visibility = "hidden";
	mov = 0;
	nub.style.top = 0;
	nub.style.left = 0;
}