In tip 0201, I described the DefaultSeparateVDM value name, which works in Windows NT 4.0 and Windows 2000.
If you would prefer to configure the ability to run a 16bit application in a separate Virtual DOS Machine (VDM) on a per user basis, you can use the Run in Separate Memory Space Group Policy at User Configuration\AdministrativeTemplates\Start Menu & Taskbar.
When the policy is enabled, typing a 16bit application into the Start / Run box enables the check box.
If the policy is Not configured, you can use Regedt32 to navigate to:
On the Edit menu, Add Value name MemCheckBoxInRunDlg, as a REG_DWORD data type. A data value of 0, the default, leaves the policy disabled. A data value of 1 enables the policy.
NOTE: If you subsequently toggle the policy from Not configured, this registry entry will be deleted, unless the policy is set toEnabled. If you then toggle the policy to anything else, the registry entry will be deleted. This is true for most policy entries.