John,
It is pretty simple to write Volume Shadowcopy Requestors once you find all the information you need to know. I've thought about putting some code and explanations up on the net. There is a major problem with XP. It only lets you create one shadowcopy. Vista and Windows 7 lets you create 64 or 256. So one of the problems I've tackles is product upgrade. If you upgrade a working product and the upgrade fails, you want to be able to get back to your original point rather that to leave the system in an inoperable state.
I've used a combination of the USN Journal to understand what has changed and the Volume Shadowcopy Service to 'freeze' a copy of the volume before you start the upgrade. Volume Shadowcopies are preserved across reboots so on Vista or Windows 7 you could create a new shadow of the volume every time you needed to reboot during the upgrade. Not so with XP. With XP you need to use the USN Journal to keep track of files that have changed, been deleted, been added, folders too.
-Scott
StCroixSkipper