>Does anyone have any advice on licensing a VFP DLL?
>I don't mean legal issues, but restricting use of the control only to machines that used our installation to install it.

You'd need to do something during your installation that the control checks for at run time; as John suggested, a registry entry written during the installation is one approach that you could use. Of course, a sufficiently determined end-user could discover the registry entry and copy it out with a .REG file, but if your main concern is to make certain that the control is properly installed, there's no reason for a user to go hunting around for stray registry keys (it'll be easier to use your installer, presumably.)

I use exactly that approach to indicate the operating mode of one of the OLE servers that I developed; the value of a registry key created during the installation by the InstallShield script indicates the operating mode of the control at that workstation. If I find that the operating mode isn't one of the legal settings that an install might have put there, the Init event returns .F. and the server doesn't get created.

There's no direct scripting in the VFP Setup Wizard, but you could use a post-setup executable to take care of writing the registry entry for you (as well as any other tasks not performed automagically by Setup Wizard.)

You aren't limited to using the registry, obviously; you could write some sort of configuration file checked by the server in a known location on the local system. The key is to have the installer leave some evidence that it did its work properly that the control knows how to find and validate before it runs.