Well, you'd have to build your form dynamically using PHP, like so:
echo '<select name="cbointdom" size="1">
<option value="%day%"' . ((@$_POST['cbointdom'] == '%day%') ? ' selected' : '') . '>All</option>
<option value="Monday"' . ((@$_POST['cbointdom'] == 'Monday') ? ' selected' : '') . '>Monday</option>
<option value="Tuesday"' . ((@$_POST['cbointdom'] == 'Tuesday') ? ' selected' : '') . '>Tuesday</option>
<option value="Wednesday"' . ((@$_POST['cbointdom'] == 'Wednesday') ? ' selected' : '') . '>Wednesday</option>
<option value="Thursday"' . ((@$_POST['cbointdom'] == 'Thursday') ? ' selected' : '') . '>Thursday</option>
<option value="Friday">' . ((@$_POST['cbointdom'] == 'Friday') ? ' selected' : '') . 'Friday</option>
<option value="Saturday"' . ((@$_POST['cbointdom'] == 'Saturday') ? ' selected' : '') . '>Saturday</option>
<option value="Sunday"' . ((@$_POST['cbointdom'] == 'Sunday') ? ' selected' : '') . '>Sunday</option>
</select>
'; // etc. etc. for all select boxes
Now, this probably won't look very pretty and may take some time, but you could actually generate more of the form dynamically using an array of possible values and a [man]foreach/man loop, like so:
$cbointdom = array(
'All' => '%day%',
'Monday' => 'Monday',
'Tuesday' => 'Tuesday',
'Wednesday' => 'Wednesday',
'Thursday' => 'Thursday',
'Friday' => 'Friday',
'Saturday' => 'Saturday',
'Sunday' => 'Sunday');
echo '<select name="cbointdom" size="1">
';
foreach($cbointdom as $value => $display) {
$selected = ((@$_POST['cbointdom'] == $value) ? ' selected' : '')
echo '<option value="' . $value . '"' . $selected . ">$display</option>\n";
}