Nowadays the Cloud is becoming an interesting distributed computing paradigm, able to strongly leverage the concept of Virtualization of physical resources. This paper deals with the opportunity to manage Virtualization Infrastructures in Federated scenarios exploiting GRID resources. In particular, the middleware we are introducing, named CLEVER, presents several features enabling an useful and easy management of private/hybrid clouds. In this scenario even GRID middle wares may benefit of CLEVER advanced features, thanks to its simple and easy accessible interfaces that enable to interact with different "interconnected" clouds. The integration of any GRID middleware with CLEVER allows administrators to easily setup a cloud infrastructure for a quick provisioning of IaaS Services on GRIDs.