Set Adobe as default program via Group Policy

You're seeing the dreaded scourge of asynchronous policy processing. It's not a "feature" (and was default-off in Windows 2000 but default-on in Windows XP and above) and causes exactly what you're seeing-- non-deterministic behaviour with processing some types of GPO settings.

In a GPO that applies to that computer, add the following setting:

• Computer Settings
  • Administrative Templates
    • System
      • Logon
        • Always wait for the network at computer startup and logon - Enabled

After you set that (and allow the GPO to replicate if you're in a multi-DC environment), do a "gpupdate /force /boot" on the subject PC. It will reboot and you should see the software installation occur.

The "Always wait for the network at computer startup and logon" slightly slows down the startup and logon because all GPO extensions are allowed to process, but the upside is that all GPO extensions are allowed to process.

Software installation policy is processed before Startup Scripts are executed. Sometimes that's exactly what you want, and other times it's not. You can't change it.

When I want a startup script to run before software installation I end up using group membership to control the execution of the startup script and I end the startup script with a command to add the computer to a second group that controls software installation. The only problem with this is that, to date, I have yet to find any reliable way to restart a Windows XP or newer OS from a startup script. (Yes, yes-- I've tried a variety of methods, too. I can discuss them in detail if you'd like.) As such, this always makes this strategy require two boots to "take effect".

You mention "preferences", so I think you're looking at doing things to the user's environment via a logon script. Logon scripts are executed, obviously, after logon. If you're looking to check to see if a piece of software has been installed during the logon script query the Windows Installer "database" in the registry to see if the program is there and "bail out". You'll find the installed products in the "HKEY_CLASSES_ROOT\Installer\Products" key. Obviously, you'll have to figure out the GUID for the package you're dealing with.

Edit: Group Policy client-side extension (CSE) processing order is performed based on the value of the GUID for the client-side extension, from what I've been able to glean from documentation. It looks like the CSE's with numerically higher GUIDs execute later. I don't have the GUID for the "Preferences" CSE handy so I can't tell you how it should act re: running before / after other CSE's.

On Windows XP, at least, dig into HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinLogon\GPExtensions and look for the CSE for "Prefernces". REGEDIT will sort those GUIDs numerically, too, so you could be able to tell, visually, if that "Preferences" CSE is going to execute before/after other CSE's.