querystring doesn't work!!!!

i have a page entitled form.php and i'm sending a string into it so it becomes form.php?expand=test now in the page i have <?php echo $expand ?> this should cause 'test' to be written to the page and indeed it does on one machine that i use, on the other (independant machine) it doesn't work and nothing is produced atall!!!?!?! I'm completely baffeled and can't work out why this is.... anyone? both machines are windowsNT both running apache and php works fine other than that , ie i can access a mysql database on either machine...