This paper presents a network design tool for ATM networks, which allows for multi-hour dimensioning of networks supporting simultaneously peer-to-peer and client-server based services. The dimensioning procedure assumes aggregation of Virtual Circuit Connections into fixed bandwidth end-to-end Virtual Path Connections. In peer-to-peer services, connections are established between all node pairs of the service. In client-server based services (e.g., video-on-demand, fast Internet access), connections are between service nodes and servers. In this case, the dimensioning procedure allows for the selection of the best server for each node. The design model is formulated as a linear integer programming problem, which is solved through a heuristic based on Lagrangean relaxation with sub-gradient optimization. This approach allows the computation of a theoretical lower bound, which is very useful in assessing the quality of the obtained solution. The network design tool includes a graphical interface for an easy introduction and edition of the network parameters. Results show that the tool can design large networks with reasonable computational speed and good accuracy.