Note that most Linux installations include a PyGTK package and some (e.g. Ubuntu) have it installed by default.
To test whether your Python installation already includes PyGTK, type 'import gtk' into a python prompt. No response means you do. However, this can be a curse as well as a blessing, because if you have an older "enterprise" linux platform
such as Red Hat or SuSE, it's difficult to put a newer GTK in place than the default. In this case you should
refer to the instructions under doc/Upgrade_PyGTK_Enterprise_Linux in the TextTest download.
On
Windows, the summary for how to install is that you should get the GTK 2.18 bundle from
here, unzip it somewhere (avoid locations with spaces in their names, I find "C:\Gtk" works just fine for me!), add its "bin" subdirectory to your PATH and then run the three installers at the top of the
PyGTK downloads page. In general neither TextTest nor PyGTK handle paths with spaces in their names well: both are ports of software written on UNIX so you're well advised to steer clear of "Program Files" and "Documents and Settings", whatever your Windows best-practice manual may tell you...
On Windows, Patrick Finnegan sent me a very nice
Windows
installer for tkdiff and diff and kindly agreed that I
could distribute it here. Note that the installer won't affect
your path though, so you'll need to set PATH in autoexec.bat or
similar to include wherever it's installed (typcially something
like C:\Program Files\tkdiff)