In this paper we report on a longitudinal study of a Leonardo da Vinci program regarding the application of a Computer Based Learning environment in three EU countries, Greece, Germany, and Holland. The `` Orestis''CD-ROM was a multimedia CBL environment aimed at teaching young offenders the basic and advanced skills for the use and maintenance of a photo-copy shop. The complete project consisted of three phases: construction of the CD-ROM, application of the instructional methodology in the participating countries and evaluation of the outcome. In this paper we firstly clarify the notion of CBL environments, in comparison to multimedia and distance learning ones, and then we provide some theoretical background on these environments. The main research question we tried to answer was whether the application of the environment under real circumstances could perform adequately without the presence of a domain expert as a ``teacher'', but rely on a ``tutor'' who had five main tasks to perform during the instructional phase, as described in the paper. In order to answer this question, we designed and constructed the aforementioned integrated CBL environment and, in addition to this, an instructional methodology in order to apply it effectivelly in the participating countries. The application of the environment by the partners showed our hypothesis about the tutor to be correct, moreover we elicited results about the different user groups that worked with the environment and their performance under different circumstances. We studied also the combination of CBL training and real practice in real environments, among some other issues concerning the application of CBL environments in general, and we provide some statistical facts as observed and reported during the two pilot studies and the five applications of the environment in the three participating European countries. We conclude by arguing that the tutor, as described in this paper, performs more than satisfactorily and demands far fewer resources than a real domain expert. However, it must be emphasized once more at this point, that this conclusion implies the application of a predefined instructional methodology that aids the tutor in his role, since the teaching procedure will be a task for the hypermedia enriched CBL environment, designed ad hoc for the intended user group and according to the appropriate educational theories.