Before you begin, you will need to install the following Perl modules which may not be part of a standard Perl installation:
Having unpacked this tar file, you should see a number of directories:
The cgi-bin directory contains files (currently just catkin.pl) that should be placed in your cgi-bin directory. catkin.pl should be edited so that the $CATKIN_DIR variable points to the directory where you placed the config files. you may also need to edit the @LIB_DIRS variable to point to the directory where you keep your Perl libraries.
The lib directory contains Perl modules which should be placed somewhere in Perl's include path (or pointed to in catkin.pl).
The config directory contains the configuration and data files necessary for a Catkin site. The contents of the directory should be placed on a part of your webserver that is not visible to the public. The config.xml file should be edited to reflect your system.
The site directory contains catkin.css, which is referenced in the default templates. Move catkin.css to the directory in which your blog will be built.
Once all this is done, you should be able to see the Catkin Management page at http://yoursite.com/cgi-bin/catkin.pl. From there you can post new entries, as well managing other aspects of your blog.
There have been some small changes to the templates. In particular, access to the date fields has changed, and the forms now use <input type="submit" ...> instead of <button>...</button>.
The format used for storing blog entries has changed. They are now all stored in a single XML file rather than lots of individual files. Use the convert-0.2-to-0.3.pl script to convert your old entries.
Catkin 0.2.x used the HTML::Template module for its templates. Catkin 0.3.x uses Template Toolkit. You will need to copy over the new templates into your config directory and, if necessary, make any changes. The old templates will no longer be used.
If you set html_ext to a value other than ".html" when you were using 0.2.x then you'll probably want to set default_ext for 0.3. Note that while html_ext required the leading period (.), this shouldn't be present in default_ext.