> I tried to continue the mirroring but the program seemed 
> to start from the beginning. An update operation was no 
> better as the web site reports that all the pages have 
> changed...

Use 'Continue an interrupted mirror', this should do the 
trick (except if you erased the cache).
Note that httrack will ALWAYS rescan the complete 
structure, even if in cache (in this case the rescan will 
not trigger any download), to rebuild its internal 
filesystem table and representation.