1. A system for supporting a dynamic scaling of applications in a transactional middleware machine environment, comprising: a plurality of physical machines comprising a plurality of transactional middleware machines in a transactional domain of the transactional middleware machine environment; a plurality of deployment agents, each of which is associated with a transactional middleware machine of said plurality of transactional middleware machines; a plurality of virtual machines wherein each of said plurality of virtual machines may be bound to one of said plurality of physical machines in order to operate said virtual machine; a plurality of different application packages embodying a plurality of different applications executable by one or more of said plurality of virtual machines; a deployment center running on one or more microprocessors in the transactional middleware machine environment; wherein the deployment center receives machine usage information from the plurality of deployment agents; wherein each of said plurality of virtual machines comprises a plurality of candidate different application packages which may be activated or deactivated on said virtual machine by said deployment center in response to said machine usage information received from the plurality of deployment agents, and wherein the deployment center is configured to automatically scale up execution of a particular application of said plurality of different applications in the transactional domain, in response to said machine usage information collected by the plurality of deployment agents, using two different mechanisms including, dynamically deploying an associated particular one of said plurality of different application packages to an operating virtual machine of said plurality of virtual machines and activating said particular application on said operating virtual machine; and binding, to a physical machine of said plurality of physical machines, a non-operating one of said plurality of virtual machines to which said associated one of said plurality of different application packages had previously been deployed, booting said non-operating one of said plurality of virtual machines and activating said particular application; and wherein the dynamic resource broker is configured to automatically scale down execution of said particular application, in response to said machine usage information collected by the one or more deployment agents, using two different mechanisms including, dynamically undeploying said associated particular one of said plurality of different application packages from an operating virtual machine of said plurality of virtual machines such that said operating virtual machine terminates executing said particular application; and unbinding, from a physical machine of said plurality of physical machines, an operating one of said plurality of virtual machines on which said associated one of said plurality of different application packages had previously been deployed, such that said operating one of said plurality of virtual machines terminates operating and terminates executing said particular application.