Hi again dadaz,
So after reinstalling my machine during the weekend I found that (which you also found) it seems that it has more to do with the ability to control the screen, (lacking of good kexts?) than the dsdt file it self. Your dsdt files might be good after all. But the catch is that the computer cannot control the screen for a proper sleep.
When I reinstalled 10.5.6 I realised that sleep didn’t work until installed the patched kexts (GMA 950, AppleIntelIntegratedFramebuffer). When I forced sleep without the kexts, it tried to sleep like Airport hibernated but that’s all. No sleepimage was written and screen was still on. When I installed the kexts, sleep worked with no problems.
So the point seems to be, that for a proper sleep, Mac OS has to control the screen, otherwise no correct sleep or wakeup. I’ll report if I find anything more on this.