Standard envir onments for exploiting idle time of workstations are base d on some kind of spying process that detects low CPU usage and informs to a scheduler so that work can be disp atche d. This approach gener ateslocal interfer enc eand, sinc e the same local envir onmentis used, could lead to security problems. We are investigating the exploitation of idle times in network resources based onacomplete mode change in a candidate node. After the dete ction that some node is idle, a Mode-Switcher boots a new operating system that will work over a separate disk partition. After the boot phase the node is linkedto a logical network topology and is available to receive jobs. Users can allocate no des fr om this virtual cluster thr ough a standard front-end as they would do in a "conventional" cluster. Because nodes may leave and join this virtual machine we use a distribute dprocessormanagement to allow user applic ationsto cope with this dynamic resour ce behavior. In this paper we describ e the architecture of the virtual cluster and present the results obtained with a Mode-Switcher and a prototyp eapplic ationunder real use conditions.