In modern distributed computer systems (clusters and computing GRIDs) a new class of problems, due to the increasing heterogeneity of users’ needs, have to be tackled by the administrators. One possible solution is to create ondemand virtual working environments tailored on the user’s requirements. Hence the need for an architecture to manage dynamically such environments. In this work we propose a possible solution based on the use of Virtual Machines (Xen), the implementation of a Virtual Machine Manager, capable of creation, destruction and migration of the virtualized working environments. The information will be collected using a client-server mechanism, to allow the manager to deploy preconfigured Virtual Machines on the available har...