I spent a couple of hours looking at your DSDT the acpi spec and my dsdt (mine is relatively clean, and tracks the mac pretty well). The bad news is that yours is a hideous monstrosity. It's massive-- more than double the size of a macbook dsdt, and several thousand lines more than mine. Plus it implements a WMID interface (see: http://www.wilsonmar.com/1wmiwbem.htm) and even as checks to make sure the BIOS isn't modified. It also seems to deliberately obfuscate some things-- I believe to lock down some aspects of HP laptops.

So while I did manage to understand some things about the brightness settings, I couldn't suggest anything for you to try, other than running it through a recent DSDT patcher and telling the patcher to emulate Windows Vista or Windows 7. Then you could try that version to see if it helps.

Alternatively, you can search Linux forms for the same issue and for the same laptop. They will likely have the same problem, however, your DSDT specifically checks for Linux. So you could also try "pretending" OS X is Linux in the DSDT and see if that helps.

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MacBook Pro - have allergy to nickel in the aluminum casing. So my kid gets an expensive toy!

Gateway MX 8738 - Retail, vanilla Snow Leopard 10.6.2 (thanks kizwan!) with Chameleon RC4, modified DSDT. Upgraded to Core 2 CPU (easy to do). Upgraded to 640GB drive. Everything but SD card working. Minor niggles. GMA950 with QE/CI and *no* artifacts.

iMac (luxo/lamp) G4 with Tiger.