AppSearch Table: Windows Installer can use AppSearch to search for a specified registry entry, file, or folder while installing your package. AppSearch searches your computer for file signatures that you specify in the AppSearch table of the Windows Installer package. If AppSearch locates a file, a registry key, or a folder that has the signature that you specified, AppSearch returns search results as a property. You can use this property to establish a launch condition. If the condition that you set is not satisfied, the launch condition quits the installation process.
This blog describes some of the packaging standards. Also contains methods to silently install different applications or handling their configuration for mass deployements.