Microsoft Knowledge Base Article 816102 contains the following summary:
This step-by-step article describes how to use Group Policy to automatically distribute programs to client computers or users. You can use Group Policy to distribute computer programs by using the following methods:
You can assign a program distribution to users or computers. If you assign the program to a user, it is installed when the user logs on to the computer. When the user first runs the program, the installation is finalized. If you assign the program to a computer, it is installed when the computer starts, and it is available to all users who log on to the computer. When a user first runs the program, the installation is finalized.
You can publish a program distribution to users. When the user logs on to the computer, the published program is displayed in the Add or Remove Programs dialog box, and it can be installed from there.
Note Windows Server 2003 Group Policy automated-program installation requires client computers that are running Microsoft Windows 2000 or later.