Open 3rd party application within same domain in new window

Hi,
I am a newbie, and I need to integrate Mantis with Drupal 6,
but because no module are currently supporting it, I modified the Mantis index page as suggested by other forum and it works.
Can you teach me how to open for example http://localhost/mantis in new window, while my drupal is in http://localhost/drupal.

Thank you very much