Computer simulation, because it can be applied to operational problems that are too difficult to model and solve analytically, is an especially effective tool to help analyse Supply/Demand Chain (S/DC) [1] capacity utilization issues [2]. As part of the ongoing research project daisy [3] has a case study for analysing the benefit of interfacing an Enterprise Resource planning system (ERP) with a system for computer simulation. Connecting simulation tools to systems for ERP in order to import necessary input data to simulate production plans would be a proper way to apply computer simulation tools to this type of problems. Simulating production plans could have different purposes, e.g. minimizing waste of resources or setting accurate delivery dates. Technically the connection between the two systems, i.e. the simulation system and the ERP system, could be made in an uncomplicated manner, for instance using files or network-based solutions. Different purposes will require different response time between the two systems involved and thereby different solutions for the connection. The main question in this study is not the technical connection but rather which data to import and the needed quality of these data in order to analyse capacity utilisation. For those ho have built real life simulation models lack of realistically data is a well-known fact. This is due to obsolete or inaccurate product data in ERP systems.