As commodity microprocessors and networks reach performance levels comparable to those used in massively parallel processors, clusters of symmetric multiprocessors are starting to be called the supercomputers of tomorrow. At the low-end of this technology are the clusters of SMP PCs, usually based on Pentium Pro or Pentium II processors. Many groups in the academia and in the industry are setting up such clusters with big expectations. However, how far can one go with a cluster of SMP PCs when the goal is high performance computing? This paper discusses several aspects regarding the adoption of clusters of SMP PCs to support high performance computing, including software and hardware restrains to deliver processing power to parallel applications, as well as the most innovative alternatives to overcome these restrains. Besides discussing the current state of PC cluster computing, the authors identify further enhancements that will help to enable these low-cost machines to join the HPC u..