This paper describes a generic infrastructure for supporting decision-oriented collaborative tasks, i.e., structured tasks in which argumentation and decision are important aspects (e.g. brainstorming, document outlining, review/inspection, concept map co-design, confrontation/merging of concept maps).The approach is mainly based on fine-grain modelling of decision-oriented collaborative tasks and the use of different assistance techniques: guidance, argumentative reasoning, group awareness. The paper describes the project objectives, the conceptual meta model, the task modelling language, and the current java prototype. This work is a first step in a strategy for the "conceptual integration" of different kinds of cooperation support through an extended modeling framework that should merge coarse-grain modeling of workflow management systems and fine-grain modeling as described here.