The goal of the presentation is to give an overview about how to build a commodity PC based GNU/Linux cluster for High Performance Computing (HPC) in research. After the presentation, the audience should be able to decide whether a source based GNU/Linux distribution is suitable for their computing needs, and how to actually install a source based computing cluster on their own. Due to the extreme flexibility of the GNU/Linux operating system and the large variety of hardware components, building a cluster for High Performance Computing (HPC) is still a challenge in many cases. At the Division of Intelligent Systems at the Norwegian University of Science and Technology (NTNU), we have build a 40 node HPC cluster for research purposes using the source-based GNU/Linux distribution SourceMage. We describe a methodology for designing and installing a highly customized GNU/Linux cluster. Different types of Linux distributions will be mentioned, binary-based and source-based, with their advantages and disadvantages. The presentation will focus on using SourceMage for HPC, specifying the 'magical' ideas behind it: the ease of upgrading to the latest available version of the source code, a packaging system for keeping track of dependencies, optimized compiles for the hardware architecture used, easy integration of new packages, amongst others. *Topics* * Why can a Beowulf-type PC cluster be used for High Performance Computing needs and how does that differ from other types of distributed and parallel computing environments? * Which type of hardware and software can be used? * Software necessary to run a PC cluster, usage of standard services. * Which libraries and tools can be used for parallel and distributed computing? * User management and security issues, job scheduling and load distribution technologies. * Aspects of node configuration and different methods for node cloning. * Cluster installation and administration. * Different concepts of booting, running, and maintaining the nodes. * The special advantages and pitfalls of choosing a source based software installation and maintenance compared to a binary based solution. * Benefits and problems in customizing the Linux kernel and other aspects of the operating system environment. *Intended Audience* Intended for scientists and engineers interested in learning about ways to set up a HPC cluster. Neither in depth knowledge of the Linux operating system, nor about clustering technologies is necessary. General knowledge about Unix type systems and parallel or distributed computing is helpful.