i found some of the info here - apparently I assumed correctly
http://msdn2.microsoft.com/en-us/library/ms790308.aspx
http://msdn2.microsoft.com/en-us/library/ms790806.aspx
below is copied from the above link
Windows Driver Kit: Device Installation
Driver Package Installer (DPInst)
Driver Package Installer (DPInst) version 2.1 is a component of Driver Install Frameworks (DIFx) version 2.1 that simplifies and customizes the installation of driver packages for devices that are not yet installed in a computer (commonly known as a software-first installation). DPInst also automatically updates the drivers for any installed devices that are supported by the newly installed driver packages.
By using DPInst, you can:
Enhance the user experience of a driver package by eliminating most of the manual steps that would otherwise be required to install driver packages. When a user runs DPInst, a wizard notifies the user of the installation progress and provides an optional end-user license agreement (EULA) page that gives the user the option to cancel installation. For more information about the wizard pages, see DPInst User Experience and Installing and Uninstalling Driver Packages.
Avoid writing a custom installation program to install driver packages and update the installed drivers for supported devices. You do not have to change your driver packages to use DPInst. You only need to create an installation package that includes DPInst and one or more driver packages. For more information about creating this type of installation package, see Creating a DPInst Installation Package.
it would seem that your program simply extracts the driverpacks and launches the MS program. 700K seems huge for that?