Love the license plates 😉
Anyhow, get into the habit of always quoting attributes in your HTML. Make the change as shown below, and see if that helps any:
<?
$id = $_GET['id'];
$width = $_GET['width'];
$height = $_GET['height'];
echo "<object classid=\"clsid27CDB6E-AE6D-11cf-96B8-444553540000\">";
echo "<codebase=\"http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=5,0,42,0\">";
echo "<id=\"".$id."\" width=\"".$width."\" height=\"".$height."\">";
echo "<param name=\"movie\" value=\"http://www.smartmindmedia.com/flash/files/$id.swf\">";
echo "<param name=\"bgcolor\" value=\"#FFFFFF\">";
echo "<param name=\"quality\" value=\"high\">";
echo "<param name=\"allowscriptaccess\" value=\"samedomain\">";
echo "</object>";
?>
Note, although it isn't required when double-quoting, I did take the liberty in concatenating the variables...