You must have python (http://www.python.org) installed first. If you want to
take advantage of the graphical configuration interface, you must have
functioning Tkinter. Fortunately, many (all?) recent linux distributions
come with python/tkinter.

Simply unpack the distribution archive in a suitable directory, set up 
configuration and run pyftpd.py.

For unix servers: you might consider setting up a dedicate user for
running pyftpd. If you want to bind pyftpd to a port below 1024, you
probably need special privileges for it (which can be achieved by
using sockfs, medusa, rsbac or something similar for linux; or running
under root privileges - this is NOT recommended)

For Windows servers: install python first. If you want graphical interface,
answer Yes when the installer asks you to install tcl/tk. If you want to get
rid of the MSDOS prompt window, rename pyftpd.py to pyftpd.pyw (in future,
this will be default, but for now MSDOS window is useful for debug and error
messages). If you want to start it automatically, add pyftpd.py to your
Start Up group.
