I've spent the past few days trying to figure out HOW to make XP with SP2 install unsigned drivers silently. Changing DriverSigningPolicy in winnt.sif still warned that the driver wasn't signed. Changing Driver Signing registry entries still warned that the driver wasn't signed. Nothing I tried would get rid of the prompt, so I finally decided to just create an AutoIt script to "Continue anyway". I've attached the script, the compiled exe, grep.exe and devcon.exe.

All you have to do to use this method (I'm sure there are other methods, but this is how I use it):

• Download the attached .rar
• Extract devcon.exe and grep.exe to $OEM$\$$\system32, DriverInstall.exe to $OEM$\$1\Drivers
• In RunOnceEx.cmd, add driver checks such as:

• Inside the IF ( ) block, invoke DriverInstaller with the relevant switches (for information about the switches that DriverInstaller supports, read about Commands for DevCon Operations), such as:

A brief breakdown about the DriverInstaller line above:
%systemdrive%\Drivers\DriverInstall.exe: The path to DriverInstaller.exe
update: Update the driver (as opposed to install, disable, enable, etc)
%systemdrive%\Drivers\002_graphics\NVIDIA\2KXP_INF\NV_OMEGA_DISP.INF: Path to the .inf for the drivers you wish to update
PCI\VEN_10DE: The hardware vendor ID. You must get this from inside the driver's .inf

Completed, my RunOnceEx.cmd looks something like:

I've tested this to work with signed drivers, unsigned drivers, drivers with multiple prompts, and it has worked each time.

Any questions/comments, feel free to let me know. Hope this helps someone as much as it helped me.

Never mind, solved it! Turns out in the most recent version of AutoIt (Since 3.0) the Opt RunErrorsFatal is gone. Take out that line, and it works beautifully.