This snippet taken from The Definitive Guide to Building a Windows Server 2008 Infrastructure, a free e-book sponsored by Tricerat. Get your free copy of the entire 10-chapter bookhere.

Yet another of GPP's powers arrives from the ability to further target GPP application based on a set of characteristics. Also seen under the Common tab is a link titled Item-level targeting. Checking this box and then clicking the Targeting button brings forward a screen similar to the image below. Item-level targeting provides you the ability to link a GPP to an Organizational Unit, but instruct the policy only to process when the client object meets a preconfigured set of criteria.

In the picture above item-level targeting has been set to only apply the GPP when the object's CPU speed is greater than 1000 MHz, free disk space is greater than or equal to 80 GB, the operating system is Windows Vista, the machine is a portable computer that is docked, undocked, or unknown, and the RAM is greater than or equal to 512 MB. Considering the options available, the level of targeting can be as granular as your needs.

To set item-level targeting, simply click the New Item button and select an item. Upon selecting an item, configure its options in the bottom pane. Click OK to complete the process. Once complete, objects will only apply the policy when they meet the targeting guidelines.