Place the "speak" executable file in the command path, eg in /usr/local/bin
Place the "speak-data" directory in /usr/share as /usr/share/speak-data. Alternatively if it is placed in the user's home directory (i.e. /home/<user>/speak-data) then that will be used instead.
Dependencies.
speak uses the PortAudio sound library, so you will need to have the libportaudio0 library package installed. It may be already, since it's used by other software, such as OpenOffice.org and the Audacity sound editor.