Hey Michael,
I have not been very closely involved with the DWH installation pain in OCI 7.3.3, but my understanding is that all the pain is due to Cognos 11.0+ switching to using an Informix database, and this Informix database is trying to create local or domain user accounts at install time to use as a service account. Therefore, the pain is resulting from environments running security hardening that prohibits user account creation and/or enforces certain password complexity and therefore is unrelated to which Windows version you are installing the DWH on.
Matt