Creo que algo asi es lo que buscas:
Código:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Dos tablas alineadas</title>
<style type="text/css">
#contenedor {
width:auto;
height:auto;
text-align:center;
float:left;
}
#encabezado {
color: #B4886B;
font-weight: bold;
text-align:center;
}
div#tabla_uno{
width:300px;
position:relative;
float: left;
height: auto;
margin-right: 10px;
}
div#tabla_dos{
width:300px;
position:relative;
float: left;
height: auto;
}
</style>
</head>
<body>
<div id="contenedor">
<div id="encabezado">
<caption>Prueba Con Tabla</caption>
</div>
<div id="tabla_uno">
<table width="300" border="1" cellspacing="1" cellpadding="1">
<tr>
<td scope="col">z</td>
<td scope="col">z</td>
<td scope="col">z</td>
</tr>
<tr>
<td><div align="center">z</div></td>
<td><div align="center">z</div></td>
<td><div align="center">z</div></td>
</tr>
</table>
</div>
<div id="tabla_dos">
<table width="300" border="1" cellspacing="1" cellpadding="1">
<tr>
<td scope="col">z</td>
<td scope="col">z</td>
<td scope="col">z</td>
</tr>
<tr>
<td><div align="center">z</div></td>
<td><div align="center">z</div></td>
<td><div align="center">z</div></td>
</tr>
</table>
</div>
</div>
</body>
</html>