If you attempt to boot into Windows PE from a Hyper-V virtual machine, you may not be able to immediately access network resources as you would expect.  This is because a default VM configuration in Hyper-V includes the synthetic network card, which is not visible to any OS that doesn't have the Integration Components installed.  To enable network functionality on a Windows PE VM, remove the existing network card from your configuration, then select Add Hardware, and choose the Legacy Network Adapter.

You'll need to remove and re-add the synthetic network adapter (listed simply as Network Adapter in Hyper-V VM settings) when you have Vista or Server 2008 installed.