1. A method for isolating access by application programs to native resources provided by an operating system, the method comprising the steps of: redirecting to an isolation environment comprising a user isolation scope and an application isolation scope a request for a native resource made by a process executing on behalf of a first user; locating an instance of the requested resource in the user isolation scope on behalf of a first user; and responding to the request for the native resource using the instance of the resource located in the user isolation scope.