Mobile computing is characterised by variations in user needs and in the computing and communication resources. We have developed a middleware centric approach for the development of software capable of dynamically adapting to such variations. The middleware leverages models of needs and resources and the adaptation capabilities of the software and performs context monitoring, adaptation planning and dynamic reconfiguration at runtime. In this paper we focus on the modelling of resources of a distributed mobile computing infrastructure and how the resource model is used in adaptation planning. We present a distributed resource management framework and mechanisms necessary to maintain an up to date resource model at runtime. The challenge is to balance the level of abstraction so as to hide some of the heterogeneity of the actual infrastructure while retaining sufficient detail to serve the needs of distributed and centralized adaptation planning. The proposed framework is illustrated through a running example.