1. An integration services network for facilitating access to a plurality of composite services by a plurality of users having associated client machines, each of the users being associated with one of a plurality of independent enterprises, the network comprising: at least one data store having a directory stored therein which maps an identity for each of the users to a policy framework which defines access information relating to a plurality of services, one or more of the plurality of services communicating with the integration services network via a public network; and at least one computing device configured to: set up a first composite service by integrating operation of a first subset of the services, integrating operation of the first subset of services including mediating policy differences between or among the first subset of services with reference to the policy framework, the first subset of services being associated with and controlled by a first plurality of independent service providers, set up a second composite service by integrating operation of a second subset of the services, integrating operation of the second subset of services including mediating policy differences between or among the second subset of services with reference to the policy framework, the second subset of services being associated with and controlled by a second plurality of independent service providers, the second subset of services at least partially overlapping with the first subset of services, provide an interface to one or more of the plurality of users, the interface allowing the one or more users to select one or both of the first composite service or the second composite service; and connect with the client machines and each of the services associated with the first and second composite services, and selectively facilitate interaction among the client machines and the services with reference to the directory and the policy framework, thereby enabling each of the users to access one or both of the first or second composite services as an integrated solution in which each of the composite services facilitates dissemination of messages between or among the corresponding subset of services.