You can change all the absolute URLS to relative into the several html files
(considering that the page those links link to were mirrored)

There are several programs, for example Notepad++. The main understanding is
to know two things:

1) If the pages linked by absolute links were mirrores, the ones you want.

2) If 1) applies, in which folders they were saved.

Also, some pages are stored on google or yahoo cache, in case you search those
engines.

Probably, you have some missconfigured options in httrack, like internal depth
to a very low value, or maybe the forum requires authentication and you are
not logged with your username in the forums in Internet Explires, or such... I
am clueless.