To Juan Quintela Just to say that I tried your kernel-2.4.20.0.5 with the "MyDsdt" integrated patch, and it just work fine. Thank you very much for thinking about people who have a "non standard" acpi implementation.
I didn't test all acpi features (like sleep or suspend on swap (yes, this one don't come from acpi patch :-) ) but for the moment I can monitor my batteries and switch off the screen (without DRI module loaded). It seems few, but it's a lot for a laptop user. Thank you again. If I can do something to help you, tell me. Sebastien. ps: enclosed is my dsdt file, it work on my 2818fr and I should work with all compaq presario 28xx
dsdt_presario_2800.bz2
Description: BZip2 compressed data
