It should work pretty well to
- Create a new Vaadin project in Eclipse
- Add the Calendar add-on jar from the Directory to WEB-INF/lib
- Add the sources from http://dev.vaadin.com/svn/addons/Calendar/trunk/demo/src/ to your project.
- Ensure that web.xml points to the correct application class
- Compile the widgetset
- Deploy
Some other Calendar examples are
- the Devoxx calendar (http://www.devoxx.com/display/Devoxx2K10/Calendar), sources at http://code.google.com/p/devoxx-schedule-2010/
- the ICEPush multi user calendar demo (http://artur.virtuallypreinstalled.com/MultiUserCalendar), sources at http://dev.vaadin.com/svn/incubator/MultiUserCalendar/