I know if you were trying to do the opposite (include vb code in wordpress or some other program), it has a problem because global.php can only be included from the current directory. So to include vb code you have to do something like:
PHP Code:
$savedir = getcwd();
chdir("path_to_vb_forum_dir");
require_once("./global.php");
chdir($savedir);
So maybe you could try something like that.