Web Server, php includes dont' seem to resolve

Well i wasn't sure where to ask this question sisnce i dont' know where the problem is.

I'm setting up a web server on freeBSD 4.9 with apache 2.0.48  and php 4.3.4 mysql is also on the server, my website is up and running on my windows box which has all the same (maybe a bit older versions but definately apache 2 and php 4.

Warning: main(/phpBB2/extension.inc): failed to open stream: No such file or directory in /usr/home/chris/webpage/php/Header.php on line 10

Warning: main(): Failed opening '/phpBB2/extension.inc' for inclusion (include_path='.:/php/includes:/usr/home/chris/webpage/php:/usr/home/chris/webpage/wwwroot') in /usr/home/chris/webpage/php/Header.php on line 10

thats the type of error i'm getting, and i can't figure out why.
the file to be includes is located at
/usr/home/chris/webpage/wwwroot/phpBB2/extension.inc

this is just one example it's hapenning with some includes.(all of them in the phpBB2 dir)

      $site_root_path = '';
      $phpbb_root_path2 = '/phpBB2/';
      $phpbb_root_path = $site_root_path . $phpbb_root_path2;
      include($phpbb_root_path . 'extension.inc');

is the code including it.

any help would be appreaciated if it has to do with nix specific stuff try to be really startight forward, just learning for the most part.

Thx you very much.
LittleGiant