I nearly leaked this ahead of time; as part of the Release Candidate for Hyper-V we have released a version of of the management console to run on Windows Vista SP1. (No, to the best of my Knowledge we don't have plans of a version which runs on XP or Server 2003 - this is Windows "6" only. )
Jeff has posted some screen shots to the Virtualization team blog
If you want to run on Server Core this means you can have the tools to manage it on a workstation without needing to install one full server machine to get them. To avoid confusion, the 64 bit Version of Vista and the x86 versions of Vista and Server CAN'T run hyper-V but CAN run the management tools for it.
Update: A new version is now out for RC-1 See http://support.microsoft.com/?id=949587