thinkpad-acpi (known as ibm-acpi up to Linux 2.6.22) can generate ACPI events (loading with hotkey=enable) for several Fn-Fx combinations, including Fn-F4, which is already supported by ACPI. However, the generated events differ from the usual events.
button/sleep SLPB 00000080 00000002
ibm/hotkey HKEY 00000080 00001004
Using gnome-power-manager and hal on etch this makes suspending using Fn-F4 impossible, because the hal does not recognize the events. The fix is quite simple; build and install hal from lenny:
apt-get source -t lenny hal apt-get build-dep hal cd hal-<version>/
Now you have to alter
---enable-acpi-ibm to the configure target and build the package using:
fakeroot dpkg-buildpackage -uc -us
After installing the new packages and their depencies (hal-info from lenny) the new hald will send
Sleep events when pressing Fn-F4 and
Hibernate Fn-F4, which makes gnome-power-manager to initiate a suspend to disk cycle.