A Thinkpad Kernel for Fedora Core 5
First of all, this kernel works for me, i.e. on a T41 2379-DJU. I can suspend to ram and suspend to disk (suspend2), all using ACPI. I think that the same kernel configuration should also work on the other T4x series thinkpads (T40/T40p/T41/T41p/T42/T42p) but I cannot verify this myself. As they say: if it breaks, you get to keep both pieces. This RPM should install in parallel with the official Fedora kernel RPM, but having a rescue CD/DVD/USB-key cannot hurt.
Quick installation: copy & paste into a root shell, and replace VERSION and RELEASE by whatever file you want:
rpm -Uhv http://carrot.hep.upenn.edu/%7Evbraun/kernel-T4x/i386/kernel-T4x-VERSION-RELEASE.i386.rpm
Update: I have set up a yum repository. Copy the repository configuration kernel-T4x.repo to /etc/yum.repos.d/ and everything should be automatic.
As root, run thinkpad-T4x-suspend. Your computer should suspend to ram. Some Thinkpads have still a rather high power consumption, but others work well (the radeon chipset does not get powered down). There is no fix that works for every radeon chipset, but you can try to enable a possible workaround with the kernel command line option "video=radeonfb:force_sleep". In any case, pressing the power button will resume your machine in a few seconds.
Also as root, run thinkpad-T4x-hibernate. The content of the ram will be written to disk and then your machine turns off. Everything is written to the swap partition, so it better be large enough to hold all of your ram (plus a bit more). Upon reboot, make sure you boot the same kernel!
I am assuming everywhere that you are using the "radeon" module for the Xorg server, Fedora detects and uses this one automatically during install. I doubt that resume will work with ATI's binary only driver.