How to make a VCL form act modally for a non VCL parent window

I am having difficulty making a Delphi VCL form act modally when the parent
window is not a VCL form.

The form in question the configuration form for a screen saver I am writing
in Delphi 3 for Win95.

I want the form to act modally when the Settings button is clicked on the
Screen Saver page of the Display Properties.

Can anyone tell me how to do this?