ATI x1600 overheating on Ubuntu 10.10 64bit, laptop
I have a friend running vanilla Ubuntu 10.10 x64 (desktop) on a Compaq nx9420 laptop, which has an ATI x1600 integrated.
He is getting severe, rapid overheating of the GPU, to over 110 C and shutdown.
He disassembled the unit, checked the heat pipes and fan etc, and reassembled, same problem.
I had him disable KMS in Grub and reboot, didn't fix it. Verified that KMS is disabled in Xorg.0.log, but even at the GDM login or in textmode using Ctrl+Alt+F1 he is getting temperature rapidly climbing over 100 C.
This behavior does not occur in Windows on the same laptop, GPU stays cool and happy.
Unfortunately that means a badly designed laptop or too much termal paste. You will never be able to use its full power without overheating, you can just keep the temperature down with powersavings.
That may be true if the OP's friend has played 3D games on windows and the computer still overheats. However, to see if you can use any linux on it, try installing Debian Lenny (the oldstable version) with ATI's proprietary drivers, or even better for testing, try to grab PCLinuxOS 2009 live CD from somewhere, after it starts just type "sudo aticonfig set-powerstate 1", and see if your laptop still overheats (it should not).
As good as the progress with OSS Ati drivers is, the driver (or whatever component it is today that does the power management) cannot keep my Mobility X1600 at its lowest temperature for a prolonged time (but it won't let it overheat, either). That's why it's still Debian Lenny for me.