Mike Sterling has just done a great post on how to integrate the Hyper-V Integration Services into a WinPE image. If you do WinPE based OS installations on a regular basis this will really speed things up for you. Read more here:
UPDATE 8/9/2010: Note that this is only necessary if you are using Windows Vista / Windows Server 2008 based WinPE. WinPE images based on Windows 7 / Windows Server 2008 R2 already have integration services in them.