Enterprise computing facilities, such as data centers or server farms typically employ service-oriented architectures (SOA) to support multiple, XML-based Web Services. They are typically architected in multiple computing tiers, in which one tier is used for, say, offloading the CPU-intensive XML processing onto a cluster of (potentially virtual) middle-ware appliances. Service differentiation in enterprise networks addresses the issues of managing the enterprise network resources in order to achieve desired performance objectives. In this paper, we define a dynamic algorithm that manages allocation of CPU time in the appliance tier. We evaluate the service differentiation capabilities of this algorithm via simulations.