1. A method for providing access to a desktop computing environment by a virtual machine launched by a hypervisor executing in a terminal services session, the method comprising the steps of: a) receiving from a client system i) credentials for a user of the client system and ii) a request for an enumeration of desktop computing environments available to the user; b) collecting data from a plurality of execution machines, the data including i) desktop computing environment images on each execution machine and ii) access control information for each desktop computing environment image; c) storing the collected data in a database; d) using the user credentials and the collected data from the database to determine desktop computing environment images available to the user; e) transmitting the collected data to the client system indicating desktop computing environments corresponding to the desktop computing environment images available to the user, f) receiving, from the client system, a request to access one of the desktop computing environments; g) selecting, by a broker machine, a virtual machine that can provide the requested desktop computing environment and a first operating system in which to execute the requested desktop computing environment; h) selecting, by the broker machine, an execution machine executing a hypervisor providing access to hardware resources required by the virtual machine; i) launching, by the broker machine, the virtual machine into the execution machine, i) the execution machine having a second operating system that provides a terminal services session, ii) the terminal services session executing the hypervisor, iii) the hypervisor executing the virtual machine, and iv) the virtual machine executing the first operating system for the requested desktop computing environment; j) launching, by the broker machine, the requested desktop computing environment into the first operating system provided by the virtual machine by deploying a desktop computing environment image corresponding to the requested desktop computing environment; and k) establishing a connection between the client system and the requested desktop computing environment.