This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Victor, To learn JUnit, "Junit in Action" and "JUnit Recipes" are excellent. (Note that both cover JUnit 3.8 though.)
For JUnit 4.0, "Test Driven Development" is excellent. I think combined with some JUnit articles from the web, you'd be fine launching right into "Test Driven Development." This stuff changes so often that I like the idea of buying a more recent book.