Extreme Programming (XP) is inherently collaborative, which makes it amenable to Computer Supported Cooperative Work (CSCW) support. The collaboration enabling tools and techniques used in XP, such as whiteboards, index cards and co-location, are adequate for their immediate purposes. However, they do not allow sufficient information to survive beyond the end of projects. Long term consequences of their use include the risk of inadequate software maintenance, and limitation of the process' scalability. In this thesis, we explore the opportunity to address these risks by means of a desktop-based client/server experimental groupware application. We exploit existing metaphors and characteristics of XP, such as the `information radiator' and the natural hierarchical arrangement of the primary project concerns, in order to reduce the gap between user's mental model of normal XP and CSCW enabled XP. We use XML, relaxed-WYSIWIS and a message passing communications system to allow users to interact with the same or different aspects of a project's information space---the Project Document---while they collaborate on essential project planning and coordination activities of the Planning Game. We conclude that our choice of deployment architecture and selection of aspects of XP which are augmented offer relevant and more sophisticated support for XP teams than do web-based approaches reported in literature.