I was in a tight spot one night after I decided to move a Windows 2008 based VM from a VMWare based host server to a Hyper-V based host.

This resulted in most of the hardware changing within the guest VM and in turn forced a reactivation of the OS. The problem was I couldn’t get past the activation dialogue to install the integration tools in Hyper-V to get the network drivers installed. No network drivers meant no network card, which meant no activation.

This article made it easy.

http://www.petri.co.il/bypass-windows-server-2008-activation.htm

Great stuff.