Not able to use the group policy in windows server 2008

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.

Use an OU - there is no such thing as a network too small to use an OU. Apply the policies to the OU as you can't apply Group Policies to the default users and computers container.

If you want to use this setup, I would create a "Computer" OU, move all the regular computer accounts to that OU and apply the default comptuer OU there. Create a child OU "MgmtComputers" OU off the Computer OU and apply just the Management computer OU there.

Edit: BTW - if you are setting "domain users" as local administrators in your default computer policy and allowing "Log On Locally" to include the administrator group, since every domain user is a local admin, it would still allow every user to login to every computer.