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 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.