Prueba si esto te funciona:
<html>
<head>
<script>
var imgsobre=new Image();
imgsobre.src="pliegueseleccion.gif";
var imgfuera=new Image();
imgfuera.src="blanco.gif";
function sobre(obj,ndi) {
obj.style.backgroundColor='#ff9966';
document.images["fila"+ndi].src=imgsobre.src;
}
function fuera(obj,ndi) {
obj.style.backgroundColor='#ffffff';
document.images["fila"+ndi].src=imgfuera.src;
}
</script>
</head>
<body>
<table>
<tr onmouseover="sobre(this,'1')" onmouseout="fuera(this,1)">
<td>Columna 1</td>
<td>Columna 2</td>
<td>Columna 3</td>
<td>Columna 4</td>
<td><img name="fila1" src="blanco.gif" /></td>
</tr>
<tr onmouseover="sobre(this,'2')" onmouseout="fuera(this,2)">
<td>Columna 1</td>
<td>Columna 2</td>
<td>Columna 3</td>
<td>Columna 4</td>
<td><img name="fila2" src="blanco.gif" /></td>
</tr>
<tr onmouseover="sobre(this,'3')" onmouseout="fuera(this,3)">
<td>Columna 1</td>
<td>Columna 2</td>
<td>Columna 3</td>
<td>Columna 4</td>
<td><img name="fila3" src="blanco.gif" /></td>
</tr>
<tr onmouseover="sobre(this,'4')" onmouseout="fuera(this,4)">
<td>Columna 1</td>
<td>Columna 2</td>
<td>Columna 3</td>
<td>Columna 4</td>
<td><img name="fila4" src="blanco.gif" /></td>
</tr>
</table>
</body>
</html>