Papyrus is a UML designer plugin for the eclipse development environment. Installing it on the Indigo version is very easy:

1. Go to Help > Install New Software…
2. Under Work with, select All Available Sites and look for Modeling on the tree view.
3. Under Modeling, look for MDT Papyrus – SDK and press the Next button
4. Press Next again
5. Accept the Licence and press Finish
6. You will be asked to restart Eclipse, so go ahead…
7. Next time you create a project, you will see the Papyrus project listed.

Happy modeling!