abre o popup com o <select> e no botão enviar você usa na página pai fica assim: <form name="form1">
<input type="text" name="txt1" readonly="readonly" />
<a href="java script:" onClick="window.open('pagina.php','Teste','width=300, height=200, scroolbar=yes');">buscar empresa</a>
</form>
no pop-up:
<script language="JavaScript" type="text/javascript">
<!--
function envia(parStr){
window.opener.document.form1.txt1.value=parStr;
self.close();
}
//-->
</script>
</head>
<body>
<select name="sl1" onchange="java script:envia(options[selectedIndex].value);">
<option value="ahahah">a</option>
<option value="eheheh">e</option>
<option value="ihihih">i</option>
<option value="ohohoh">o</option>
</select>