A major problem in requirements engineering is obtaining requirements that address the concerns of multiple stakeholders. An approach to such a problem is the Theory-W based Spiral Model. This paper focuses on the problem of developing a support system for such a model. In particular it identifies needs and capabilities required to address the problem of negotiation and renegotiation that arises when the model is applied to incremental requirements engineering. The paper formulates elements of the support system, called WinWin, for providing such capabilities. The key elements of WinWin are described and their use in incremental requirements engineering are demonstrated, using an example renegotiation scenario from the domain of software engineering environments, for satellite ground stations.