Are you sure that Fn+F2 doesn't work? On my Dell, it appears to be hardware controlled (it works no matter what distro I have running, but the LED doesn't).
Wen not sure because I've recompiled a new kernel and the /proc/acpi/asus sutff has dissapeared .... it may work but I bet it will not untill I compile a 2.6.25.1 kernel that gets me back the stuff in /proc/acpi/asus.
OK I think I figured out what was wrong in my kernel:
in order to make the CONFIG_ASUS_LAPTOP option come out I neaded to fix up these dependencies...
depends on X86
depends on ACPI
depends on EXPERIMENTAL && !ACPI_ASUS
depends on LEDS_CLASS
depends on BACKLIGHT_CLASS_DEVICE
I'm building the kernel right now ;-)