Select File -> New -> Project, HiberObjects - HiberObjects Project.

This will create a new Java project with the HiberObjects nature enabled. It will set up 3 source directories: src, test and conf. An initial class diagram can be created.
The HiberObjects project properties page is used to configure a HiberObjects project, but it can also be used to add or remove HiberObjects capabilities from an existing Java project.
Right-click on the Project and select Properties. In the project Properties dialog, select HiberObjects and select Enable HiberObjects functionality.

To configure Hibernate or JPA, select the Persistence page:

Platform may be one of the following:
Open the Project Explorer view: Window -> Show View -> Other, and then select General - Project Explorer.

A HiberObjects node shall be visible in the project. Designed packages, diagrams and classes will be displayed under this node.

Note: This does not work in the Package Explorer or Projects view, only in the Project Explorer.
Note: If nothing shows up, try the Customize View... command in the view menu, go to Content and make sure HiberObjects is selected.