I'm reasonably new to Group Policy administration and I'm trying to deploy an 
MSI installer via Active Directory to install a service.  In reality, I'm a 
software developer trying to test how my service will be installed in a domain 
environment.
My test environment:
Server 2003 Domain Controller
About 10 machines (between XP SP3, and server 2008) all joined to my domain.
No real other setup, or active directory configuration has been done apart from 
things like getting DNS right.  I suspect that I may be missing a step in Group 
Policy that says I need to grant an explicit permission somewhere, but I have no 
idea where that might be or what it will say.
What I've done:
I followed the documentation from Microsoft in How to Deploy Software via Group 
Policy, so I believe all those steps are correct (I used the UNC path, verified 
NTFS permissions, I have verified the computers and users are members of groups 
that are assigned to receive the policy etc).
If I deploy the software via the Computer Configuration, when I reboot the 
target machine I get the following:
When the computer starts up it logs Event ID 108, and says "Failed to apply 
changes to software installation settings.  Software changes could not be 
applied.  A previous log entry with details should exist.  The error was: An 
operations error occurred."
There are no previous log entries to check, which is weird because if it ever 
actually tried to invoke the windows installer it should log any sort of failure 
of my application's installer.
If I open a command prompt and manually run:
msiexec /qb /i \\[host]\[share]\installer.msi 
It installs the service just fine.
If I deploy the software via the User Configuration, when I log that user in the 
Event Log says that software changes were applied successfully, but my service 
isn't installed.
However, when deployed via the User configuration even though it's not installed 
when I go to Control Panel - Add/Remove Programs and click on Add New Programs 
my service installer is being advertised and I can install/remove it from there. 
(this does not happen when it's assigned to computers)
Hopefully that wall of text was enough information to get me going, thanks all 
for the help.