dFold is command line only. Unpack the file that you download and then move the resulting distribfold folder to wherever you want it.
Before you run the program you will need to get your handle. Go to:
http://distributedfolding.org/login.html
and sign up. You will then be sent and 8 digit handle. If you then go back to the same place you can log in and join Team MacNN.
I would guess that right now they have no power as the site seems to be dead.
Open a terminal window and cd into that directory. If you are hazy on how to do that type cd, drag the folder to the terminal window and then hit return. Then type "./foldit". You will then be asked a bunch of questions including what your handle is. Other questions:
Use more RAM: no means that you will use about 32MBs of RAM, yes means from 60-150MBs depending on the protein.
Autoupdate: just say yes.
Quiet: Yes means that there will be no output to the terminal. You should probably say no to this until you have run it some.
Internet connection: Yes if you have an always on connection. You can answer yes even if you have a modem but it will time out for 1 or 2 minutes each time that it tries to connect when the modem is off.
There are some more questions but those are the main ones. (that I can remember) There is a readme1st.txt file in the directory that has a lot of info, or even too much.