The local registry values that affect Group Policy and software installation logging are:
The following registry setting enables verbose logging of GPO processing to the computer's Application Event Log. Note that in Win2K these events show up as Informational events, while in XP, they appear as Error events.
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Diagnostics
RunDiagnosticLoggingGroupPolicy DWORD 1
The following registry settings log GPO processing to the file C:\Windows\Debug\UserMode\userenv.log. Note that the modes of logging presented here are just a few of the options. For more information, see http://support.microsoft.com/kb/221833.
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
No Logging: UserEnvDebugLevel DWORD 0
Normal Logging: UserEnvDebugLevel DWORD 0x10001
Verbose Logging: UserEnvDebugLevel DWORD 0x10002
The following registry setting logs software installation and upgrade decisions made by the Group Policy engine to the file C:\Windows\Debug\UserMode\appmgmt.log.
HKLM\Software\Microsoft\Windows NT\CurrentVersion\Diagnostics
AppmgmtDebugLevel DWORD 0x9B
The following registry settings log all Windows Installer actions. Group Policy initiated software installation is logged to files named %windir%\temp\MSI*.log, and user initiated software installation is logged to files named %temp%\MSI*.log
HKLM\Software\Policies\Microsoft\Windows\Installer
Logging STRING voicewarmup
Debug DWORD 0x3
For more information on diagnostic logging for Group Polcy, see http://technet.microsoft.com/en-us/library/cc775423.aspx.