I installed a Microsoft Hyper-V Server a couple of days ago. Hyper-V Server is a version of Windows Server 2008 core that includes the Hyper-V role, all other roles are disabled. There is a new simple interface to configure the server. You can also use the Hyper-V MMC and System Center Virtual Machine Manager to administer your Hyper-V server. More info about Hyper-V Server here.
I installed an agent from Operations Manager 2007 without any problem. However I found out that Ops Mgr found the machine as 2008 full installation (installation type = full), not as a core machine (installation type = core). Not the worst thing, but it is good to know. You can see it if you create a new state view target Windows Server 2008 Computers.
I also tried to install a Data Protection Manager 2007 agent on my Hyper-V server. First DPM could not identify my Hyper-V server as a known Windows version. In Active Directory I could see that my Hyper-V server operating system is set to “Hyper-V Server”, not “Windows Server 2008 Enterprise” as my other core machines. When I changed it to “Windows Server 2008” there was no problem adding it to DPM and installing the agent. I guess that the DPM query does not recognize “Hyper-V Server” as a supported operating system, but that works too after this “workaround”.