As of Base 8.05 dpinst.exe is included and copied during the slipstream
this makes any DriverPacks slipstreamed disk a drivers only disk, in addition to its normal function.
Bâshrat the Sneaky called this feature a 'SAD disc' or Stand Alone Drivers disc.
we are exploreing other options for this tool as well, stay tuned...
Since DPInst is a Microsoft redistributable file lets start with their description...
http://msdn2.microsoft.com/en-us/library/ms790308.aspx
http://msdn2.microsoft.com/en-us/library/ms790806.aspx
text below is copied from the above links
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.
Very Microsoft-eze, In simple terms;
It updates Windows drivers at any time - not just during an install - It could be post install...
and this is how we use DPinst.exe - we add it to the OEM folder. (or $OEM$\$1\ for M1)
We also add a small script file in the same folder.
The script prepares the DriverPacks in the same way as it would for the method used to create the disk
(Method One or Method Two is "staged" the same as DriverPacks would do it.)
then DPinst is called from the script.
DPinst is the missing link we have been searching for to add drivers to an existing installation of windows, or update them:
It checks the current machines device manager, and compares its drivers to what is in the DriverPacks
If newer drivers are found in the DriverPacks than exist in the target machine then it's drivers are updated
- on the fly - Unattendedly.
Now, if that is not pretty darned slick all by itself... let me just toss this in for a bonus;
Since we have prestaged the drivers in exactly the same way as DriverPacks would the DP_Finisher will run exactly as it would if you had just done an unnatended install (except we didn't, we just dropped our disk in any computer)
The finisher calls keep the driver (KTD) and cleans up the packs and removes all traces of the driverpacks. (just like normal)
note: It applies whatever KTD settings exist in the source OEM folder.
So what we have after all the smoke and mirrors is a way to install DriverPacks on any system (BlackBox) at any time.
THE SCRIPT IS \OEM\DP_Install_Tool.cmd (or \$OEM$\$1\DP_Install_Tool.cmd for M1)
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It's a one click solution to update ANY win2k winxp or win2k3 box with the DriverPacks!
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can you say... Have a nice day! 
PS normal installation of DriverPacks does not need or use DPInst.
PSS you could use AUTORUN.INF to call DP_Install_Tool.cmd 
(might want to add a pause at the beginning of the script if you do 
)