// IP to country start
        require_once( '/path/to/ip2c.php' );
        if ( !empty( $cur_post['poster_ip'] ) )
        {
            $ipc = new ip2country();
            $ipc->init( '/path/to/ip2cntry.dat' );
            $idx = $ipc->lookup( $cur_post['poster_ip'] );
            if ( $idx != IP2C_IP_NOT_FOUND )
            {
                $ccode = $ipc->idx2country( $idx );
                $user_info[] = '<dd><img src="/path/to/flags/' . 
                    strtolower( $ccode ) . '.gif" style="width: 16px; height: 12px;" alt="' . 
                    $ccode . '" />';
            }
            unset( $ipc );
        }
        // IP to country stop

Remember to change the /path/to.

This requires our ip to country for PHP, and the world.small flag-pack from ip-to-country.webhosting.info!