I have a page that I need to php include a file only IF a category has been selected.

I'm not sure what syntax I need to use, I've tried both the following:

PHP Code:
<?php
   if ($cat1=='')
   echo "Test";
   if ($cat1!='')
   include ("gallery.php") ;
   ?>
and

PHP Code:
<?php 
$cat1 = $_POST['cat1'];
if (!isSet($_POST['cat1'])){
  echo "<p>Please choose a category!</p>";
  }
if (isSet($_POST['cat1'])){
include ("gallery.php") ;
}?>
Both echo the statements when the category is not selected and both display the file regardless...

Any advice would be appreciated!