This is what I did for a template page I created for a similar situation.
<div id="content" class="hfeed">
<?php the_content(); ?>
<? echo "<h1 class=\"entry-title\">Category Filtering</h1>";?>
<div id="category-options">
<form method="post" action="">
<p><input id="papers" type="checkbox" name="papers" value="Featured Paper, Feature Papers, Second Edition, Second Editions, Student Paper, Student Papers" <? if(isset($_POST['papers'])) { echo "checked"; }?>><label for="papers"> Papers</label></p>
<p><input id="articles" type="checkbox" name="articles" value="Commentary, Commentaries, Articles, Advisory Article, Advisory Articles, Series Article, Series Articles" <? if(isset($_POST['articles'])) echo "checked"; ?>><label for="articles"> Articles</label></p>
<p><input id="book-reviews" type="checkbox" name="book-reviews" value="Book Review, Book Reviews" <? if(isset($_POST['book-reviews'])) echo "checked"; ?> >
<input type="hidden" name="cats" value="1"><label for="book-reviews">Book Reviews</label></p>
<input type="submit" name="submit" value="Submit">
</form>
</div>
<div id="category-results">
<?php
if(isset($_POST['cats'])) {
$cats = "";
$comma = ", ";
//check if the papers checkbox was clicked and update the categories to filter by
if(isset($_POST['papers'])) {
$cats = mysql_real_escape_string(htmlentities($_POST['papers']));
}
//check if the articles checkbox was clicked and update the categories to filter by, accordingly
if(isset($_POST['articles'])) {
if(strlen($cats) > 1) { $cats = $cats.$comma; }
$cats .= mysql_real_escape_string(htmlentities($_POST['articles']));
}
//check if the book-reports checkbox was clicked and update the categories to filter by, accordingly
if(isset($_POST['book-reviews'])) {
if(strlen($cats) > 1) { $cats = $cats.$comma; }
$cats .= mysql_real_escape_string(htmlentities($_POST['book-reviews']));
}
$str = '[mediacat cats="'.$cats.'" orderby="date" order="DESC"]';
echo do_shortcode($str);
?>
</div>
<?php } ?>
</div>
