An important aspect of virtualization is the actual management: as an administrator, you want to have a single console for managing all your virtual machines and hosts. With software such as VMware’s VirtualCenter, you can manage a complete ESX environment and add a ton of extra features (such as DRS, HA, intelligent placement, templates, etc). Microsoft’s answer to the management question is System Center Virtual Machine Manager (also known as VMM).
This piece of software is your one-stop shop to all your Virtual Server 2005 R2 (and in the 2008 release) Hyper-V hosts and even your VI3 infrastructure. VMware’s VirtualCenter can be added and so ESX hosts can be managed from within VMM. Virtual Machine Manager 2008 provides most VirtualCenter Server functionality including VMotion. More complex tasks such as adding hosts to an ESX cluster must be done using VirtualCenter itself.