Hello Jan and Sailor Steve!
(Thanks Sailor Steve for your kind welcome) !
To Jan, I did not install the DirectX from the Silent Hunter disk. But my version is 9.0c (4.09.000.0904).
I went to Google to see how to revert backwards if a newer version of DirectX causes troubles, and it seems that it is a major chore! I also read about a tool called Nhancer here. And in the Ubisoft forums, a guy (in an old thread) mentioned setting the "stock" Catalyst settings.
I clicked the 3D settings in the Catalyst to "default", started up SH3, and got the perfect result as in the Mafia 1 trick. So I am very happy!
(I am not going to upgrade the Catalyst at this time because my computer really runs many games well, including old Windows 98 games, SH3 is otherwise showing no graphics glitches, so I don't want to spoil a good thing)!
I salute you fellows!
And thanks very much Jan Kyster for your suggestions!
Robert P.