I have a Dell Latitude C800 laptop, A23 BIOS (latest) and 1400x1050 resolution
display with an ATI Rage Mobility M4 chipset.  I have posted in the Ubuntu
forums (username sigmason) a question and gotten at least one response of
similiar behavior from a Latitude C600 series owner (with the 1600x1200 display.)

My primary Linux distro on this laptop is (k/x)ubuntu 6.06LTS, but I have
verified this behavior in a Mandrake 9.2 based pclinux distro boot CD-ROM.

My bug is pretty straight forward, at least on the Dell model with this chipset
(earlier models in the i8k series) there are issues with any display mode below
1280x1024.  You can use 1280x1024, 1400x1050, and 1600x1200 (even virtual) but
you cannot use 1024x768, 800x600 and 640x480 (and probably not the TV out
related modes either) without having to to a Fn&F7 (if you are singlehead) or
Fn&F8 (if you are dualhead) (note you have to do this as many as 3 times to get
results) key combo on the laptop keyboard.  If you don't you get artifacts
(similiar to an incorrect modeline) on the screen.  Once you do, the problem
vanishes, until you change terminals using CTRL/ALT/Fx or exit that display
mode...at which point you must repeat the procedure.

I have noted that the DDC driver gets a Level none and cannot fetch information
from the LCD panel.  I have also noted that at least in (k/x)ubuntu the DDC
driver incorrectly fetchs duplicate information for the unknown laptop display
from the second SVGA port if in use and in dualhead mode.

I have seen a note on the RedHat site that this MIGHT be corrected with
MetaMode, but have yet to find a work around, to the untrained eye this fault
mode make the laptop video appear to be broken so it's not a little issue.
Please review the Ubuntuforums.org site for the my query and links to the RedHat
report I am describing.

I have verified this is NOT a modeline issue in anyway.  To do this I used
PowerStrip in a dual boot config on the same laptop with Win2KPro and an
certified ATI driver, in the 1024x768 mode I looked at the advanced timing
register which is effectively the information in the CRTC register bank, using
that information I calculated my mode line, verified it with gtf an even tried
xvidtune.  Further, I tried the modeline provided by KDE for this display, and a
generic CRC.  I also tried about 120 other modelines for the 1024x768 mode, all
valid...all resulting in the same incorrect visual output.