I see a bunch of problems here.
First off, try using a more specific subject line when posting to forums, it may get you help sooner.
In your form tag, don't put variables in the action URL. Use hidden fields instead, like you did further below.
In your form tag's action URL, $selectdate is just that. You need to use <?php echo $selectdate ?> instead in order to get PHP to process $selectdate. Again, you did it correctly further below.
This won't work because it's in the wrong place:
<? $selectedate = $year . "-" . $month . "-" . $day; ?>
The snippet of code you've posted is what generates the form. When the form is being generated, $year $month and $day will not be set, because the user hasn't had a chance to specify them. You need to put that code in meetings.php, because that is where the form (with the date) will be submitted to.
Finally, don't use $year $month and $day. It may work, but could stop working if you upgrade PHP or change hosting providers. Use $_POST['year'] instead. Read the [man]register_globals[/man] manual page for more info.