Project planning in the Architecture, Engineering and Construction (AEC) industry at present relies heavily on individual skills, experience and improvisation. In an attempt to increase predictability and efficiency, and to improve knowledge retention across projects, this thesis proposes a more systematic approach to project planning. It does so by introducing the notion of a meta-process model that embodies and cultivates the logic and intelligence of incremental and collaborative planning activities in a given domain. Planning tasks are encoded and enforced as a set of structured dialogues between project partners. To make this possible, a taxonomy extension to current workflow modeling technology is introduced. The concept of the chosen approach can thus be classified as process mediation through structured dialogues. It is applied to the particular example case of Design-Build project delivery for which a detailed workflow model was created. This model serves as a partial instantiation of the larger Project Management Body Of Knowledge, an abstract framework put forward by the US Project Management Institute. A prototype system architecture is devised as an extension to an existing collaborative virtual environment developed in the European e-HUBs research project. This experimental Web-based platform supports the enactment of workflows that are expressed in the standardized syntax of the neutral process definition language XPDL. The functional richness of the structured dialogue extensions is demonstrated through a dialogue management prototype developed as a separate MS Access database application.