I talked about this briefly last week -- if you want to administer Hyper-V using PowerShell, what options do you have?

WMI

Hyper-V proffers some functionality through WMI classes in the “root\virtualization” namespace. You can access the raw WMI classes from PowerShell using examples like in my talk, or you can use the great library James O'Neill has uploaded to CodePlex: PowerShell Management Library for Hyper-V

Ben Pearce is doing a series on scripting Hyper-V with WMI which you should definitely check out.

System Centre Virtual Machine Manager 2008

SCVMM is a new product that will be releasing soon. It offers a unified management interface and set of services for managing a datacenter full of virtual machines. It is an additional product purchase, and so not everyone will have it.

I haven't used them, but apparently SCVMM's PowerShell cmdlets are a lot more natural to use than WMI. Further information about the PowerShell interface is available in this Scripting Guide.

Ultimately, you'll need to evaluate both approaches to see which one fits. WMI-based scripts will probably be usable in more situations, but SCVMM scripts will be easier to author and maintain.

Kirk