Look & Feel > Manage Skin Sets & Templates > Manage Templates in IP.Board
Global Templates -> defaultHeader

Change this :
<a href='{$this->settings['board_url']}' title='{$this->lang->words['go_home']}' rel="home" accesskey='1'><img src='{parse replacement="logo_img"}' alt='{$this->lang->words['logo']}' /></a>
to this:
<a href='{$this->settings['board_url']}' title='{$this->lang->words['go_home']}' rel="home" accesskey='1'><img src='{parse replacement="logo_img"}' alt='{$this->lang->words['logo']}' /><img src='{parse replacement="logo_img1"}' alt='{$this->lang->words['logo']}' /></a>
If needed you can change width and address of the images...