How i can integrate phpbb with codeigniter

[eluser]mahmood rehman[/eluser]
i have worked for 6 months in codeigniter but now i am confused how to call the phpbb functions in codeigniter.because for calling their funcions you have to include the root path and include the files.how i include the specific files into codeigniter and use thier funcntions like add user, login etc
thanks in advance