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 debian/rules: add ---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.