The virtual PHP files only allow a limited set of PHP code to be executed. You can view the allowable function calls by clicking on the gray
Limited PHP Code in the upper right corner of the PHP options pages.
That being said, there is a way to get around it. You can create a widget area where you want your slideshow to appear, then drag a text widget into it, paste your PHP code into the text widget, and then install a plugin called
Exec-PHP (HT to JuggleDad) so your PHP code will execute.
To create a widget area, insert a call to dynamic_sidebar with the name of your new widget area, for example:
<?php dynamic_sidebar( 'Widget Area Meteor' ); ?>
I would probably put a DIV around it with a unique ID so you could pretty it up in the CSS files later.
Save your options, then go to Appearances > Widgets and you should see your new widget area there (i.e., Widget Area Meteor), waiting for you to drag in a Text widget. Then just paste in your Meteor PHP code and you should be set.