Well, since my last post on WinPE Mike Sterling has blogged how to add the intergration components (the new name for Virtual Machine Additions) to a WinPE image. This means that virtual networking breaks the legacy network adaptor limit of 100MBit and our deployment of images fly through rather than sitting around twiddling their thumbs!

http://blogs.msdn.com/mikester/archive/2008/05/30/using-the-hyper-v-integration-components-in-winpe.aspx 

I only wish i'd thought of it as it's kind of an obvious thing to do to speed things up.