Problema ComboBox Dinamico

[acoevil]

Colocalo fuera del while

<select name="xx" id="xx"><option value="<?php $rs['pai_id'];?>">Select a country </option>

<?php
$listarcom="select pai_nom,pai_id from pais order by pai_nom asc";
$ejecutar_listarcom = mssql_query($listarcom,$con);
while($rs = mssql_fetch_array($ejecutar_listarcom,$base)){
echo "<option value='$rs[pai_id]'>$rs[pai_nom]</option>";

}
?>

</select>

$rx=$rs['pai_id'];