Screen blacks out for a second every minute - YDL with Radeon Mobility 9600

[Bruce]

Well, I finally got YDL going on my Powerbook G4 15" with Radeon Mobility
9600...

...but every minute or so the screen blacks out for a second or two,
before blinking back to the desktop.

The installer's graphics probe suggested 'unsupported generic vga' but
that didn't work at all. I then followed the YDL site's instructions to
choose 'generic of compatible' graphics card (ATI Radeon Mobility 9600
wasn't an option), and set it to 1mb. This works but has the black-outs.
Should I try 64mb? 

The installer probe also suggested the Titanium 15" display - which I
chose. There is no option for an Aluminium 15" display.

I would appreciate any suggestions.

Regards,
Bruce