You can force it to default OUs, by applying it at Domain level, you can not phyiscally link it to the standard Computer, and User containers...cause they are only containers and not OUs..
Over the weekend, I will be posting some FAQs on here about common Group Policy and Active Directory problems. Such as configuring Group Policy for Domains and minimising replication sizes.
Download the new GPMC for Win 2003 if you haven't already done it. This is the Group Policy Managment Console, and Group Policy Object Editor for Win 2000/2003 domains. There is a tool in there called the Group Policy Modelling Wizard. It is pretty self explanitory, just make sure when it asks you to specify a user and machine...specify a sing user "domain\JBlogs" and a single machine "domain\AcMachine018" rather than groups. This will shows every exact setting that is being applied.
I am also in the process of writing a guide book to accompany Group Policy.
Check back for Updates.
Hope this Helps.
Neil J Cotton
njc Information Systems
Systems Consultant