IDS works well in a Microsoft Cluster environment and has had dedicated code to handle cluster failover for several years. There is also a utility called ClusterIT which was designed to make IDS cluster set-up on Windows easier, but Windows clustering generally is one of those areas where the Informix documentation has always been a bit thin.
Thomas Matthae - the guy who created ClusterIT - recently wrote a developerWorks article entitled IDS and ClusterIT -- How to set up Informix in a Microsoft Cluster Environment which redresses the documentation gap. It has an overview of the Windows Cluster environment, the Cluster Administrator, and goes through a step-by-step installation of IDS in a clustered environment.
IDS in a Windows Cluster environment