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 can start playing around with Hadoop using just a single Linux box. You can run Hadoop in a single machine using local mode or using pseudo-distributed mode to test/debug your MapReduce programs. Using a cloud offering like Amazon EMR is another way to get going.