> I try to mirror some '.tgz' filesfrom 
> <http://ftp.back2roots.org/geekgadgets/baseline/>
> but the file on the local mirror doesn't match:

This is because the http server sees .tgz files as gzip-
encoded-files (tar+gzip), replying with proper headers, and 
then httrack decompress them when the download is finished.

What you get is in fact .tar files.