Windows 2000 includes Windows Installer technology, which makes installing and maintaining applications easier than with Windows NT 4.0. Windows Installer consists of two components: an OS service and a package file that installs with applications that support Windows Installer technology.

The Windows Installer Service
Win2K uses the Windows Installer service to oversee and manage application installation. Windows Installer reads information from application package files and uses that information to perform all installation tasks, including copying files to the hard disk, making registry modifications, creating shortcuts, and prompting you for information. The OS— not the application— makes these changes, so you can restore the system to its original state if the installation fails. Windows Installer also makes sure that an application doesn’t change or delete DLLs that other applications need. If an application doesn't perform correctly after installation, it can query Window Installer for missing or deleted files and attempt to fix any problems—giving us self-repairing applications.

The Windows Installer Package File
Windows Installer package files, which have .msi file extensions, work with Windows Installer to serve as an application's setup program. Package files are relational databases that contain instructions—information about registry settings and files—for installing and uninstalling applications. When a package file runs, the Windows Installer service consults the package file and uses the information it finds there to begin installing the application. You can use transform files, which have .mst file extensions, to modify the package file's installation database and customize an installation. If an application has problems after you install it, right-click the application's package file and choose Repair from the menu that appears, and Windows Installer will compare the settings specified in the package file with the system configuration and attempt to remedy any differences.

Creating Your Own Windows Installer Packages
Unfortunately, most existing applications are legacy applications that won't include vendor-provided package files. To create package files for these programs, you must use a software repackaging tool such as WinINSTALL Limited Edition, which you can find in the Win2K installation CD-ROM's Valueadd\3rdparty\Mgmt folder. From a reference machine preferably running only W2K Professional, use WinINSTALL to create a snapshot of the system configuration. Next, install and configure the application, and take another snapshot of the system. Finally, WinINSTALL will compare the differences between the two snapshots and use this information to build a Windows Installer package file for the application. You can also use this tool to modify an existing package file to meet your needs.

After you have created or obtained your package files, you can make them available through the traditional network share or you can use Group Policy's software distribution capabilities to automate installations. To enjoy the full functionality of Group Policy’s software distribution capabilities, you must use package files. For more information about configuring Group Policy for software distribution, see Group Policy and Software Management.