upgrade from debian etch to debian testing (lenny) results in garbled screen

[Hartmut Niemann]

Hello everybody!
I upgraded the following system from debian etch to current testing:

AMD Athlon(tm) XP 2600+
VIA KT400 chipset
ATI Technologies Inc RV280 [Radeon 9200 SE] (rev 01) (according to lspci)
BENQ G2400W (1920x1200)

and the xorg.conf that worked fine with debian etch results in a totally distorted screen,
with diagonal stripes that have about the color the screen should have 
(light blue for the login screen, and the main colors of the background picture
after a more or less blind login seemed right) Like the rendering engine 
has a different opinion how many pixels are in a line from the output stage.

Interesting: the cursor had the right shape and did move with the mouse.
The resolution that the display's OnScreenDisplay lists was right as well.
please have a look at:
http://www.nieleute.de/xorg.conf.etch

I tried the xorg.conf that knoppix 5.1.1 provides as well, same result.
http://www.nieleute.de/xorg.conf.knoppix5.1

Replacing the ati driver with vesa gives me a working 1280x1024 at 75
and allows me to access mail again :-)

Versions of debian packages:
xserver-xorg-video-ati    1:6.9.0-1+

Is this version of the driver broken for my hardware?
Is my hardware broken?
What can I do? How can I provide more information to track this down?

Should this be put into the debian bug database? 

With all the best wishes to everybody for 2009
Hartmut Niemann