The computer suspends to RAM when idle only in runlevel 1.
In runlevels 2,3,5 nothing happens. apmd writes nothing to
the log, so I suppose that the BIOS does not even start
suspending. Suspend to RAM on Fn-Esc (and on closing the
display) works correctly.
The BIOS is set to some minutes of suspend time-out when on
battery power (suspend to disk is off).

To make things more mysterious, a similar BIOS action -
switching off the display when idle - works normally in
runlevel 5 (the back light goes off).

The computer is Dell Latitude C640, BIOS A07,
SuSE Linux 8.2 with APM (kernel 2.4.20-4GB, apmd-3.0.2-286),
runs kde 3.1.

Maybe somebody knows a solution.
Thanks in advance.