1. Download Eclipse
2. Add MDT project
Help > Software Updates... > Available Software > Add Site...
http://download.eclipse.org/modeling/mdt/updates/releases/
see http://www.eclipse.org/modeling/mdt/updates/
choose "MDT UML2 SDK 2.1.1"
or alternatively
eUML2 at http://www.soyatec.fr/euml2/installation/manager.ganymede.php
http://www.soyatec.com/update/ganymede/