Update on thread. I decided to upgrade the Sony Vaio with the dead Radeon chip to Karmic (9.10). The failsafe screen is now 1024x768, which matches what xp does. I have tried a series of xorg.conf settings using the "headless" setup in "Linux Format" LXF128, p.104-105. Of course the
command didn't work, because the Radeon chip is dead. If I insert what appears to be the correct settings for a widescreen sony vaio below in the Monitor section of xorg.conf, I get the segmentation fault that happens when an attempt is made to access the dead radeon chip.
# 1280x800 @ 60.00 Hz (GTF) hsync: 49.68 kHz; pclk: 83.46 MHz
HTimings 1280 1344 1480 1680
VTimings 800 801 804 828
Flags "-HSync" "+Vsync"
The xorg log shows that the glx drivers are loaded, which is the probable cause of the segfault, even though I have quoted out the glx module in xorg.conf.
So at this point, I don't have anything further that I can think of, unless someone knows how to change the default settings in the debconf database for the failsafe option, or can think of another approach. At least now under Karmic, the screen is a usable size, even though I lose the widescreen and a thin line at the top and bottom. So for once, an Ubuntu upgrade fixed something instead of borking a half dozen things that worked in the previous version.