The following link is to the Apache tutorial on setting up a clustered node instance of Hadoop.
If one has a machine (or a small handful of machines) with enough RAM and CPU cores, VMware or VirtualBox could easily be used to simulate a larger cluster of nodes.
This document describes how to install, configure and manage non-trivial Hadoop clusters ranging from a few nodes to extremely large clusters with thousands of nodes.
To play with Hadoop, you may first want to install Hadoop on a single machine (see Single Node Setup).
Via: Apache Hadoop