I have noticed that kpowersave now tells me,
Set Brightness Supported: no
There are keys on my keyboard to control the screen brightness that work so I was wondering what I can do to let kpowersave take control of that. Where would be a good place to start looking?
you need a driver in the kernel for the hardware. Right now, these are the ACPI drivers that support brightness settings and the powerbook PMU drivers. Additionally you need a small patch in powersaved to support your new hardware driver, but this one should be easier.
It is working on Toshiba, some SONYs, IBM Thinkpads, ASUS (all IIRC).
In your case, the BIOS probably handles your brightness buttons (as it does on my hp nx5000) and there is not much the software can do about this setting.