problems with combo

[rul]

i have a form with a few combo boxes, that they are filled from the db, i know how to fill them but i want to know what can i do to select one of the values of the combo by default, because this combo has female and male, but i want that when the user open the page it fills the combo and then place it on male or female depending what he choosed before in the registration page

     <select name="sexo" class="Box">
                  <? while ($row=mysql_fetch_array($rsexos))
                  {?>
                  <option value="<?=$row["id_sexo"]?>">
                  <?=$row["descripcion"]?>
                  </option>
                  <?}
                  ?>
                </select>

[br__ken]

// make $sex=the post for sex, using id or whatnot

$sex="female";
// or $sex="id#";
$sex_array=array("male","female","other");
echo "<select name='sexo'>";
foreach($sex_array as $k=>$v)
{
	// if sex=male/female/other, send a selected 
	// string, otherwise, don't
	$sel=(($sex==$v)?" selected":"");
	echo "<option value=$k $sel>$v\n";
}
echo "</select>";

[rul]

yes, i did something like that

<select name="sexo" class="Box">
<?
while ($row=mysql_fetch_array($rsexos))
{
if($row["id_sexo"]==$row2["id_sexo"])
{
echo "<option value=".$row["id_sexo"]." selected>";
echo $row["descripcion"];
echo "</option>";
}
else
{
echo "<option value=".$row["id_sexo"].">";
echo $row["descripcion"];
echo "</option>";
}
}
?>
</select>