Mine

<html>
<head>
<script>
	var visorTexto;
	function mostrar(codigo) {
	    var divMostrar = document.getElementById("div" + codigo);
	    var spanMostrar = document.getElementById("span" + codigo);
		var anchoDiv = divMostrar.offsetWidth;
		var anchoDentro = spanMostrar.offsetWidth;
		if (anchoDiv<anchoDentro) {
			visorTexto.innerHTML = spanMostrar.childNodes[0].nodeValue;
			var altoDiv = divMostrar.offsetHeight;
			var posXactual = 0;
			var posYactual = 5;
			while (divMostrar != null) {
			    posXactual += divMostrar.offsetLeft;
			    posYactual += divMostrar.offsetTop;
				divMostrar = divMostrar.offsetParent;
			}
			var maxAncho = window.document.body.clientWidth;
			var anchoVisor = (anchoDentro > maxAncho) ? maxAncho : anchoDentro;
			if (maxAncho < posXactual + anchoVisor) {
				posXactual = maxAncho - anchoVisor;
			}
			visorTexto.style.left = posXactual + "px";
			visorTexto.style.top = (posYactual + altoDiv) + "px";
			visorTexto.style.width = anchoVisor + "px";
			visorTexto.style.visibility="";
			visorTexto.style.display="block";
		}
	}
	function ocultar() {
			visorTexto.style.visibility = "hidden";
			visorTexto.style.display = "none";
	}
	function cambiaAncho() {
		document.getElementById("cuerpo").style.width = document.getElementById("ancho").value + "px";
	}
	function iniciar() {
		visorTexto = document.getElementById("visorTexto");
	}
</script>
</head>
<body onload="iniciar();">
<span id="cuerpo" style="position: absolute;">
	<table cellpadding="0" cellspacing="5" border="0" style="width: 100%;">
		<tr>
			<td style="width: 50%;" onmouseover="mostrar(1);" onmouseout="ocultar();">
				<div id="div1" style="width: 100%; border: 1px solid #FF0000; overflow: hidden;">
					<span id="span1" style="white-space: nowrap;">
						qweqwe qweqwe qweqwe qwe1
					</span>
				</div>	
			</td>
			<td style="width: 50%;" onmouseover="mostrar(2);" onmouseout="ocultar();">
				<div id="div2" style="width: 100%; border: 1px solid #FF0000; overflow: hidden; white-space: nowrap;">
					<span id="span2" style="white-space: nowrap;">
						qweqwe qweqwe qweqwe qweqwe qweqwe qwe qweqw eqwe qwe qw2
					</span>
				</div>
			</td>
		</tr>
	</table>
</span>
<div style="position: absolute; top: 200px;">
	<input type="text" id="ancho">
	<button onclick="cambiaAncho();">Cambia</button>
</div>
<span id="visorTexto" style="position: absolute; z-index: 1000; background-color: #0000C0; color: #FFFFFF; visibility: hidden; display: none;"></span>
</body>
</html>