Only available in Windows Vista Business, Enterprise, and Ultimate editions:
Group Policy Object Editor is an MMC snap-in that you can use to edit
Group Policy objects (GPOs). After GPMC is installed, you can open Group
Policy Object Editor from GPMC.
You can find this MMC snap-in in the following location:
%windir%\System32\gpedit.msc
To open the local Group Policy Object Editor, click Start, click Run,
and then type gpedit.msc.