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.
You need to add an ItemListener, not an ActionListener to obtain combo box selection events. You'll need to implement an itemStateChanged(ItemEvent e) method in which you can retrieve the selected combo box value via e.getItem(), and then populate your text area with that.