nested echo and includes, mixed html / PHP

Hi PHPers! I'm doing a simple page build by: - reading file.html into $string - reading variables into $array and then: echo (strtr($string, $array); The file.html held in $string contains some PHP <?php include("file.inc") ?> and file.inc also has some PHP <?php echo("this is inside file.inc)"; ?> I'm doing this to assemble the page via little 'modules'. This is not working, e.g. the PHP in $string is not getting parsed by PHP before being output to the browser, although I DO see the PHP in the resultant page source...any ideas? Any comments welcome! regards, jaxon