Graphics card unrecognized, poor display resolution on 10.1 RC1

Hi,
I have recently installed SUSE 10.1 RC1 on my new notebook (Amilo Pi
1536), and the only major issue remaining now concerns the rather poor
resolution of 800x600 I have with my display. The failure seems to be
specific to the SUSE setup, because an alternative try with Knoppix
gave me a better resolution of 1024x768; according to the manufacturer
data***, the screen should be able to display 1280x800. The reason
might have to do with the fact that Knoppix uses XFree86 4.3.0.1
whereas SUSE uses X.org 6.9.0. Related to this is that at installation,
the graphics card (ATI Mobility Radeon X1400) was not recognized, and
ATI's own driver could not be installed (compilation failed when I
tried the most recent download).
The original xorg.conf from SaX contained some entries in the "Screen"
section which looked like this:
SubSection "Display"
Depth 16
Modes "default"
EndSubSection
However, the Xorg.0.log told me that "default" was not defined, so that
it chose 800x600 for some reason. I hoped to resolve the problem by
replacing Modes "default" by
Modes "1024x768" "800x600" "640x480"
but this shows no effect, although the Xorg.0.log now affirms that it
should be ok (see bottom of this post for the relevant log sections
from the X.org and XFree86 trials).
Finally, I tried to change the resolution in the KDE Personal
Settings->Display, but the only result of this was a distorted screen
image.
There must be a solution to this, and it is probably not too
complicated, but I don't know what to try beyond what I have done. So,
as always, I am hoping that someone here has some good advice for me.
Tom

The Xorg.0.log showed the following after editing the modes line:
(II) Setting vga for screen 0.
(**) FBDEV(0): Depth 16, (--) framebuffer bpp 16
[...]
(II) FBDEV(0): hardware: VESA VGA (video memory: 3750kB)
(II) FBDEV(0): checking modes against framebuffer device...
(II) FBDEV(0): mode "1024x768" ok
(II) FBDEV(0): mode "800x600" ok
(II) FBDEV(0): mode "640x480" ok
(II) FBDEV(0): checking modes against monitor...
(--) FBDEV(0): Virtual size is 800x600 (pitch 800)
(**) FBDEV(0): Mode "1024x768": 61.9 MHz (scaled from 0.0 MHz), 46.0
kHz, 58.0
Hz
(II) FBDEV(0): Modeline "1024x768" 61.89 1024 1080 1184 1344 768
769 772 794
(**) FBDEV(0): Mode "800x600": 36.9 MHz (scaled from 0.0 MHz), 36.0
kHz, 58.0 H
z
(II) FBDEV(0): Modeline "800x600" 36.88 800 832 912 1024 600 601
604 621
(**) FBDEV(0): Mode "640x480": 23.1 MHz (scaled from 0.0 MHz), 28.8
kHz, 58.0 H
z
(II) FBDEV(0): Modeline "640x480" 23.06 640 656 720 800 480 481 484
497
(**) FBDEV(0): Display dimensions: (330, 210) mm
(**) FBDEV(0): DPI set to (61, 72)

By contrast, the XFree86.log from the attempt with Knoppix shows the
following, where the Virtual size is set correctly:

(II) VESA(0): Total Memory: 256 64KB banks (16384kB)
(II) VESA(0): Monitor0: Using hsync range of 28.00-96.00 kHz
(II) VESA(0): Monitor0: Using vrefresh range of 50.00-75.00 Hz
(--) VESA(0): Virtual size is 1024x768 (pitch 1024)
(**) VESA(0): *Built-in mode "1024x768"
(**) VESA(0): *Built-in mode "800x600"
(**) VESA(0): *Built-in mode "640x480"
(++) VESA(0): DPI set to (75, 75)
(II) VESA(0): Attempting to use 75Hz refresh for mode "1024x768" (117)
(II) VESA(0): Attempting to use 72Hz refresh for mode "800x600" (114)
(II) VESA(0): Attempting to use 73Hz refresh for mode "640x480" (111)
(**) VESA(0): Using "Shadow Framebuffer"
(II) Loading sub module "shadow"
(II) LoadModule: "shadow"
(II) Loading /usr/X11R6/lib/modules/libshadow.a
(II) Module shadow: vendor="The XFree86 Project"
compiled for 4.3.0.1, module version = 1.0.0
ABI class: XFree86 ANSI C Emulation, version 0.2

.