You just need to have network connection between 2 nodes (computers). They need to have different names and need to visible from each other. What operating system are you going to use?
PS: It would be much better to have computers with absolutely the same CPUs, operating systems, utilities and so on. In other case you may have issues with compatibility of different libraries, program versions...
You'll need a Ethernet network to communicate the PCs and some Operating System. You can use MS Windows HPC or Linux+Provisioning System.
Actually, a Provisioning System makes copies of the software stack and installs the same copy in each node, so it isn't mandatory for a 2-node cluster, but it's good to have one.
If you want to use a Linux system, you can check the recipes we are creating for the Intel Cluster Ready program: http://software.intel.com/en-us/articles/intel-cluster-ready-recipes/ These recipes are step-by-step instructions for installing a Linux cluster complying with the Intel Cluster Ready specification, but you can adapt the recipes to your needs.
There are plenty of short tutorials for simple 2-4 node installations, such as those for MPICH2 on Windows. In the similar linux situation, there's not much to do but get passwordless ssh running between each pair of nodes, then run Intel MPI installer, or build and install OpenMPI, for example. You can save learning about cluster provisioning as a later step, for when you connect a serious number of nodes.
Everything you need to do to run an MPI application is: 1. Connect your PC with ethernet and disable Firewall 2. Install Intel MPI Library on both nodes (you may try other MPI implementations as well) 3. Compile HelloWord test case from the test directory (test.c or test.f) (on BOTH nodes in the same location) 4. Run an application like 'mpiexec -hosts 2 name1 4 name2 4 ./example.exe' (starts 8 processes - 4 on each node) 5. Report here if you fail to run.