Let's use this article to provide quick Hyper-V tasks in PowerShell.

Get a list of virtual machines on a Hyper-V parent

# This can be run locally or against a remote parent. Use "." for local 
$VMs = gwmi MSVM_ComputerSystem -computer "<computername>" -namespace "root\virtualization" 
ForEach ($vm in $VMs) { 
   if ($vm.name -ne $vm.elementname) {    #skip the parent's name 

From the above, we can see that the list of $VMs is a list of objects. To get an object for an individual VM, we can go use:
$vm = Get-WMIObject MSVM_ComputerSystem -namespace root\virtualization -filter "ElementName = 'vmname' "

To start a VM we need to change its EnabledState to "2". So:
$vmName = $args[0] 
if (! $vmName ) { 
   $vmName = read-host "Which Virtual Machine do you wish to start? "  
$vm = gwmi -namespace root\virtualization Msvm_ComputerSystem -filter "ElementName='$vmName' " 
if ( $vm.EnabledState -eq 2 ) { 
  write-host "The virtual machine $vmName is already running." 
} else {  

Shutdown a single virtual machine on the local parent
# Shutdown a virtual machine. Based on initial idea from Tony Soper.    
# Expects a VM name as an argument, or prompts for the name. 
$vmName = $args[0] 
if (! $vmName ) { 
   $vmName = read-host "Which Virtual Machine do you wish to shut down?"  
write-host "Shutting down $vm for system maintenance"  
# Get the VM by name and request state to change to Enabled  
$vm = gwmi -namespace root\virtualization Msvm_ComputerSystem -filter "ElementName='$vmName'"   
# Get the associated Shutdown Component  
$shutdown = gwmi -namespace root\virtualization  -query "Associators of {$vm} where ResultClass=Msvm_ShutdownComponent"   
if (! $shutdown ) { 
   write-host "Virtual machine $vmName is already shut down."  
} else {     
# Initiate a forced shutdown with simple reason string, return resulting error code  
return $shutdown.InitiateShutdown($true,"System Maintenance")  

To Create a VHD:
$vhdsvc =  gwmi -class "Msvm_ImageManagementService" -name root\virtualization
$DynVHD = $vhdsvc.CreateDynamicVirtualHardDisk("E:\Test\Test-Sys.vhd", 120GB)    #Create 120Gb Dynamic VHD
$FixedVHD = $vhdsvc.CreateFixedVirtualHardDisk("E:\Test\Test-Data.vhd",40GB)  #Create 40GB Fixed VHD
$vhdJob = [wmi]$FixedVHD.job        # Job Status for creating the VHD

For more Hyper-V powerShell scripts, such as List virtual machines in a hyper-v host cluster Seehttp://social.technet.microsoft.com/wiki/contents/articles/hyper-v-scripts.aspx

A really useful module for use with Hyper-V and PowerShell is on CodePlex at: http://pshyperv.codeplex.com/

See Also