query string / variable problem

I've installed windows binary version of PHP version 4.2.0 running under Apache as a SAPI module. I'm having problems when i'm trying to pass variables between scripts and wonder if this is a configuration issue. I've included details below - a link in a file main.php <a href='download.php?id=$data->id_files'>Download</a> passes an id variable pulled from a database. this works correctly because when clicked the address bar then displays the query string variable - /blob/download.php?id=1 however in my download.php script a test for a value in the variable $id_files fails despite this having been set. if ($id_files) { I've had a similar problem with another script which opens a pop-up window to display a full size version of an image - javascript:photo_open('photo_display.php?photo=".trim($photos[$i])."', code in the new window fails to detect any value for the variable photo. Thanks, Steve