asi te refieres:
<form name="formulario" action="destino.php" target="ventanaForm" onsubmit="window.open('', 'ventanaForm', '')" method="post" >
<p><input type="text" name="eso" size="20"></p>
<p><input type="submit" onClick="window.open(this.href, this.target, 'width=300,height=200'); return false;" value="Submit" name="B1"><input type="reset" value="Reset" name="B2"></p>
</form>