This paper addresses two important needs. The first one is the need to alleviate the resource discovery task across digital repositories by subject, which includes the ability of searching heterogeneous sources that apply to a specific audience (e.g. engineering academics) or purpose (e.g. research, teaching) from one access point. The second need is to provide toolkits for federated searching which are able to be embedded in electronic learning environments used by lecturers, students and researchers. Most of these environments are institutional Virtual Learning Environments (VLEs) and Portals. Our study will show that the satisfaction of both needs faces important obstacles. On one side, standard exchange formats such as Z39.50 or OAI, developed precisely to facilitate the transfer or sharing of data between computer systems, present obstacles that make the harvesting and searching of data from digital repositories a challenging process. On the other side, VLEs are often restricted in their ability to allow the sharing and re-use of external e-learning sources discovered by federated searching toolkits. A solution for these obstacles, based on a service-oriented architecture approach, is suggested and explored on a pilot system. The aim of our research is the realisation of the concept of flexible federated searching. The intention is that the VLE user should be able to use whatever search tool he/she likes for whatever repositories he/she needs to search, without concern for how the tool and the repositories manage to communicate, or how the tool makes search results available to other VLE components. The pilot system attempts to demonstrate that most of the flexible federated searching concept can be achieved by making proper use of current interoperability standards for digital repositories and e-learning systems.