With the VI toolkit you can automate standard management tasks like cloning, moving, starting or stopping virtual machines and hosts true PowerShell. VI Toolkit takses advantage of the exisiting VMware Infrastructure SDK and translate it into a PowerShell interface.

http://www.vmware.com/sdk/vitk_win/index.html?src=EM_0803_VMW_OTHER_VITOOLKIT_DOWNLOAD

After you have installed PowerShell and VI Toolkit on your computer, you have to add the VI Toolkit powershell snapin:

# List the snappins you allready have installed:
PS C:\> get-pssnapin

# List registered snapins:
PS C:\> Get-PSSnapin -Registered

# Add the VMware.VimAutomation.Core snappin:
PS C:\> Add-PSSnapin VMware.VimAutomation.Core

# Connect to your Virtual Center server:
PS C:\> Get-VIServer x.x.x.x -User admin -Password xxxxxxx

# List virtual maschines who are powered on:
PS C:\> get-vm | Where-Object {$_.powerstate -eq ‘PoweredOn’}