To run a mirror, you need a web server that can handle CGI, and Python 1.5.2 or higher. If you want to have authenticated users, you need to use some external mechanism that sets the REMOTE_USER environment variable (such as Apache's Basic HTTP Authentication) - if you don't use this, the user is always "GuestUser".
First of all, download the latest version of the script via CVS (oh, yes, I forgot to mention - you probably need CVS as well), using the following commands:
{{{cvs -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/unitywiki login
cvs -z3 -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/unitywiki co unitywiki}}}
Copy the file unity.py into wherever you keep CGI scripts (if neccesary, changing changing the extension to ".cgi"), and modify the variable "code_dir" to the absolute path of the directory you checked the script into. Other configuration changes go in a file called "_UnitySite.py" - see "UnityConfig.py" for details.
A snapshot of the current Wiki files can be downloaded in gzip'd tar format via the URL http://www.srcf.ucam.org/~rgh22/archive.cgi?unityfiles .