Hi Tony,
The sources in the repo are part of the 5.0 release, but we use a different versioning for the Activiti Designer which is currently 0.6.0.
If you are getting dependency problems, it may depend on the Eclipse Helios distribution you're using. I know the Eclipse Modeling and the Eclipse RCP distributions should work. In addition you need to install the Eclipse Graphiti framework and the EMF feature. Let me know if you run into problems. I also try to add a wiki page about checking out the designer code in the next couple of days.
Best regards,
Tijs Rademakers
Lead developer Activiti Designer