I prefer to use extract on a tested $GET array, then a switch to choose where to go.
include 'head.html';
$_GET ? extract($_GET) : $action = '';
switch($action)
{
case '':
include 'default.html';
break;
case 'file1':
include 'file1.html';
break;
//etc, etc ...
}
include 'foot.html';
This does require that your query take the form of ...file.php?action=file1, but it works, it's easily expandable (ie, if you want to add a new page), and a bit easier to read (in my own opinion - but then, I wrote it.)
If you really want to use explode, then your issue might be that you are accessing the wrong element of the resulting array, ie: I believe your array becomes
array[0] = 'http://..../file.php'
array[1] = 'filename'