at first, search the forum! find the uncountable amount of answers for logins:
<http://httrack.kauler.com/help/CatchURL_tutorial>

apart from that, i'd suggest try to login on the htaccess level, save the
cookie file, copy it to the httrack dir and then try the --catchurl option
with the url of the 2nd login.
or try it with the cookies file after both logins are done, maybe it works