> Is it possible to configure in httrack that only
> download the new/update files from the server? 
It already does that.
For existing files it asks the server 'has this file changed?' and only
redownloads it if true. 
I get about 3 files/second on update (size independent) on most sites.
The main exceptions are 1) Webmaster reloads part of the site and forgets to
keep the timestamps. The server then reports a newer date and HTT has to
redownload. 2) Dynamic html files (index?ID=xx) are created on the fly rather
then redirecting to current fixed content - they always have a new timestamp.