Something I get asked a lot and actually this is a great and valid question so let me swing back in time a little and lets look where MPS Came from and what it was designed for.
1999: MPF is born and released as the provisioning solution for the First iteration of what is now the Solution for Hosted Messaging and Collaboration. Since this solution build on top of Exchange Server, Active Directory is a must. The target audience back then and to some extent today are larger hosters and the Phone Companies of this world, so reliablility and security and scalability were major design goals.
That said MPS can run in a minimal server configuration of 3 servers for MPF but you will not get reliability or scalability out of it because you have multiple points of failure which are not mitigated. Also keep in mind that the 3 servers only pertain to MPF and the Webservices not to the rest of the Servers required to host services like Exchange, SQL, Web and LCS Servers.
The Configuration would look something like this ...
Server1: Active Directory (recommended to have two of these)\Server2: SQL Server 2000 SP4 and MPF Engine Server (recommended to split the roles for better performance and support for multiple Engine Servers)Server3: MPS Frontend server (recommended to have at least 2 for loadbalancing)
Plus any servers for the services you plan to host.
NOTE: The above configuration is NOT recommended for production use but is suitable for Test and Development Environments.
That said we are working on a scaled down version of HMC for a future relase, as far as Windows Based Hosting goes you can scale it down pretty well since it is designed to be modular.
As always if you have any questions feel free to post them here.
Until next time