Here is a neat little snippet of PowerShell:

Get-VM | ?{$_.State -eq "Running"} |  Get-VMNetworkAdapter | Select VMName, IPAddresses

If you run this on a Hyper-V Server it will give you a listing of all the IP addresses that are assigned to running virtual machines:

This works whether you are using DHCP or Static IP addresses – and can really help when you are trying to track down a rogue virtual machine.

Cheers,
Ben