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.
Just about every possible operation is shown with examples in the POI documentation, including opening an XLS file, accessing a sheet, creating a new workbook and sheet, and saving it. Does that cover what you need to do?