I think I want to do the same thing. I am trying to mirror 
a site that I am a member of. On certain sections of the 
website it asks for a username ans password. I tried 
puting my cookies in the project folder but httrack does 
not mirror those pages that you need a password for. Below 
are the errors I am getting.

17:53:41 Error:  "Authorization Required" (401) at link 

robots.txt rules are too restrictive, ignoring /