In wireless sensor networks, localization is one of the key issues in many applications, where a number of wireless sensor devices are used, for instance, to locate one or more (moving) targets. Typical examples are pursuer/invader applications, where the wireless devices are spread over an area and have to collectively determine the position of an invader based on sensor information available on the devices. This paper presents practical results concerning two of the key issues in the deployment of localization services in wireless sensor networks: the selection of appropriate sensors for collecting the data used in the localization algorithms and localization algorithm itself. We are showing some practical results concerning both issues and compare some of the algorithms we have used in our experiments.