Q:

PerUser install with Custom Action - UAC disabled

I'm using WiX to generate an MSI that installs a browser plugin on a perUser basis. I have a custom action to install a driver using DPInst (which needs elevated privileges).
The install works fine when UAC is enabled; Windows shows the prompt to elevate. However, if I have UAC disabled and try to install on a regular user account, dpinst.exe will get spawned until the computer freezes. (About a thousand times at last count).
In the <InstallExecuteSequence> I have:
<Custom Action="Install_Drivers" After="InstallFiles">NOT Installed</Custom>
My custom action is:
<CustomAction  Id='Install_Drivers' Execute='deferred' Directory='DRIVERS'  ExeCommand='"[DRIVERS]DPinst.exe" /SW /SA' Return='ignore' Impersonate='no'/>
I have Return='ignore' because, from what I understand so far, dpinst.exe always returns a non-0 code. 
How can I ensure that the custom action fails correctly when UAC is disabled? On a related note, can I show a custom message to the user when the driver installation fails?
Further Information: I'm developing on Windows 7 currently, but targeting WinXP and up.
Edit Taking a look at the log for the installation these seem to be the relevant lines:
Executing op: CacheSizeFlush(,)
Executing op: ActionStart(Name=Install_Drivers,,)
Executing op: CustomActionSchedule(Action=Install_Drivers,ActionType=3170,Source=C:\long_redacted\Drivers\,Target="C:\long_redacted_path\Drivers\DPinst.exe" /SW /SA,)
Disallowing shutdown.  Shutdown counter: 0
CustomAction Install_Drivers returned actual error code 1073807364 but will be translated to success due to continue marking

The bit about the shutdown is, I believe, when I logged off stop the installation. (Canceling doesn't seem to have any effect).

A:

Installing a driver is an inherently per-machine operation. A limited user can't do it. So with UAC disabled, it's not going to work. DPInst apparently doesn't get the hint that it doesn't have permissions and can't get them. Sounds like a bug in DPInst. You should change your installer to be per-machine and add a launch condition on the Privileged property to prevent the installer from starting for limited users without UAC.

