Its easy and free! I found this as i had some... "fun" ... machines to convert.
It uses bartpe (a "free" counterpart to win pe) as a base and expands on it.
Some has it even running on vistaPE.
So visit them here and make sure to donate some money if you like their work. i know i do 
Generally they have good info on VM's and how to configure them or rescue them.