This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You can use Hibernate with Portlets like you do in a typical web application. If you are using Spring Portlet MVC (or Spring in the middle-tier), then it is quite simple to use Hibernate for persistence because of built-in support in Spring for integrating with Hibernate ORM.