The production of a desktop VR package to be used by trainers and educators of mentally disabled subjects who seek employment in sheltered factories has been the goal of an EC funded project named VIRT. Three virtual training environments featuring a warehouse, a workshop and an office allow the trainees to practice with typical tasks such as the assembling and the handling of materials and goods. The virtual environments are flexible and can be easily changed to create variants of the basic tasks or to change their level of complexity. The warehouse and the workshop have been extensively tested by 20 disabled workers who had no previous exposure to VR and who worked under close supervision in two Italian sheltered factories during the late period of development. Every trainee spent 96 hours practising on the VIRT-Factory Trainer environments. This activity greatly contributed to the refinement of the product and to the collection of data concerning issues such as learning of procedures and tasks, adaptation to the interaction devices and system responses, and transfer of skills. Learning was apparent even in subjects with rather severe mental insufficiency. Initial difficulties with the interaction devices were greatly diminished after a few weeks of training in all subjects. There is also initial evidence from group analyses that transfer of skills to analogous real tasks may occur. Tutors reported an increase in motivation for work in all participants, which did not change with time. It is concluded that desktop VR training can be proposed to assist the training of mentally disabled workers and that it may produce both specific and unspecific favourable effects. The package is now being distributed to interested institutions and professionals for an additional extended assessment.