Ditz stopped working when I upgraded to Ruby 1.9.2 so I'm currently working on bringing it up to scratch for 1.9.2.
Make sure you have the yaml_waml gem installed. Clone the git repo.
gem install yaml_waml
git clone git://github.com/ChrisKempson/Ditz-for-Ruby-1.9.2.git
cd Ditz-for-Ruby-1.9.2
ruby setup.rb
ditz --version
Ditz is currently falling over if there isn't a release set. This can be fixed by adding a release
ditz add-release