How to include vbulletin EXTERNALLY?

[jacksony]

I know it has been discussed, however I am still quite doubtful about this.. How do I correctly include a vbulletin into an external php page?

I tried adding this in the external script:

chdir ('/var/www/vhosts/*******.com/httpdocs/forums');
require_once('./global.php');
include('./index.php');

But it is just showing a white screen, with error:
<b>Fatal error</b>: Cannot redeclare class vB_Bootstrap_Forum in <b>/var/www/vhosts/nanzinc.com/httpdocs/forums/includes/class_bootstrap.php</b> on line <b>1443</b><br />

Even if i remove global.php line, it don't shows

Pls advise! Thanks!