Power down from software
By compiling in APM to the kernel
If you have a modern ATX motherboard with APM power support compiled in, then "halt" will powerdown the system.
The Kernel compile options for APM under 2,2,x are found in "General Setup" "Advanced Power Management BIOS support".
After you have rebooted into the new kernel or loaded the
modules, then the
halt command or
shutdown now -h will result in the machine turning itself off.