Changing Group Policy settings for one Security Group only. (Win2003 Server)

I am new to Windows Small Business Server 2003, and am slighly confused with the group policy settings. What I want to do, is set up my own Security Groups and User Templates, with their own group policy settings. (e.g. one template might be able to do accomplish one task, but another user template would be restricted and wouldn't be able to do this task)

I have found in the Console Tree of Server management, if you expand Advanced Config., then expand Group Policy Management, you can change settings for the whole domain, but not just for a specified user or group. This is not what I wanted (or even expected), because if I was, say, change the settings on the Task Scheduler, these changes apply to all users including the Domain Administrator account which I dont want. (It should have full access to the domain) (e.g., if i changed 'Prohibit creation of tasks' to enabled, the administrator would not be able to create tasks.)

Many thanks.

matty