The following is quoted from "Windows 2000 Registry" (last revised 2001) [link (excerpt)]: "
If you miss the familiar Program Manager interface from Windows 3.1, you can still use it in Windows 2000. To configure Windows 2000 to launch the Program Manager interface when Windows 2000 launches, you need to specify the shell program you want to run. Enter Program.exe for this key to launch Program Manager. What does Program Manager look like running on Windows 2000? Figure 6-2 provides you a look.
Figure 6-2: Program Manager running on Win2k (snapshot)
see also "you can temporarily change the Windows shell from Explorer.exe to Progman.exe" [more like this]