When referring to Open Source Software (OSS) components, researchers, coders and managers do not feel comfortable in defining them as COTS. Many discussions have been aimed to decide whether or not OSS can be considered a COTS without reaching the unanimous consensus of the different international communities. This paper abandons any theoretical aspect of that question and focuses on the practical steps to follow when assembling component-based systems using also OSS components. All the activities normally performed when integrating COTS in a in-house built software are reviewed with the intention of underlining if the availability of the source code (and its possible exploitation) makes any difference. Moreover this article analyzes all the activities to perform when using OSS in a component-based system that are not necessary when using COTS. The purpose of this paper is to provide a guideline for the correct use of OSS within component-based systems, and not to answer whether OSS are considered or not COTS, leaving this task to the reader.