For those who remember, I started another thread about problems with a Matrox Millenium and a psone screen.
Finally, I decided to drop those old-timer cards and I bought a "not so old but yet old enough" Powercolor Radeon7000.

Guess what ? It works fine ! Got it for 40 Euros (guys, do your maths!).
I'm not sure this information will help a lot here, but anyway, here are the appropriate Powerstrip settings for my config (screen is a BigBen Interactive 4" psone screen, PAL standard) :

Horizontal scan rate : 16
Front Porch : 42
Sync width : 96
Back Porch : 78
Vertical scan rate : 25
Front Porch : 42
Sync width : 4
Back Porch : 22

Csync ON
Horizontal and vertical polarity : +
Interlaced ON

This should give a pixel clock around 15.150.

Works fine here. I hope this helps.

(Now picture quality is another issue, I guess this screen is not so good as the original SOny screen...)

Have fun !