According to the Web site where the .NET Framework setup is available, .NET can be installed on Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000 and Windows XP, both Home and Professional Editions. As far as I know, the Windows Update for all of these versions of Windows shows the .NET Framework as one of the things that can be installed. These are the two methods that the user can use to install the .NET Framework on their machine in preparation for running an application that requires .NET. In addition, you can write a setup program or author a Microsoft Setup Information (MSI) file that includes the .NET Framework.
Any of these options put the .NET Framework on a user's machine. In other words, yes, each client machine must be upgraded to a version of Windows that supports the .NET Framework as well as upgraded to have the .NET Framework installed before executing a .NET application.
This was first published in November 2002