Here is how I use it.

• What I want to do: (1) log in, read email, etc. (2) copy files from psion to host machine.
• It is important to switch from "Terminal+New p3nfsd" to "Terminal only", otherwise it is all very slow (this was true under version 4.3 anyway). This option is under the Unix-protocol menu in version 5.1.
• One way to copy data is to use Bring.
• Trying to get xmodem working.... Rudi says:

  Nfsc only uses the Psion builtin X/Y modem support. The S3c is rumored to
  have Z-modem support built in.
  The X-modem is a quite primitive protocol.
  Y-modem extends it with the capability to send more than one file along with
  the filename. Z-modem is a more advanced (i.e. faster) protocol, but needs
  more memory for his windows, thats why the early psions did not had it.
  
  rz belongs to the only X/Y/Z-modem package I know for UNIX, it is hard to
  understand, and the newer versions are copyrighted.
  It consists of two programs: rz (receive zmodem) and sz (send zmodem). If
  you rename sz to sb then it uses Y-modem as default, if you call it sx,
  it runs the X protocol.
  If you try to send a file from the unix to the psion, you should start
  "sx " in the UNIX-shell, then return to the psion, and receive it 
  using the 128 byte (default) X modem protocol. As you are using X-modem,
  you have to give the local file a name.
  I only got the X-protocol working as far as I remember.