I just checked www.berry4all.com
and it seems that what you downloaded just contains python scripts. So, you just need to unpack it. From the looking at the downloads page it looks like the file you have is probably: bbtether-0.3q.tgz
The instructions on http://www.berry4all.com/install
It seems you are stuck at "extract it wherever you want".
Try something like the following in a terminal:
tar xzf bbtether-0.3q.tgz
The above assumes you have cd'd to the directory where you placed the file.
After that continue to follow the instructions on http://www.berry4all.com/install
and post back if you run into trouble again.