Following Doug's suggestion, I tried ACPI.PSD /VW instead of OS2APIC: now I have 3,5 Gb of RAM, 2 processors running and APM. A full boot to WPS takes less than 30 seconds...
Actually, I think that /VW was Lars' suggestion, but it was a good suggestion. ACPI does seem to work okay, with the /VW parameter. That probably means that the problem has something to do with IRQs above 15, which is a very minor thing compared to power control.
Now, both of my laptops are running with full memory, a RAMDISK that is using memory that is otherwise useless, and I have power control.
Using IRQs above 15 is "kind of nice", but totally unnecessary in almost all cases. There is probably a very small performance hit, but nothing that a user would ever notice. Hopefully, walking_x can look at his code, and spot a problem, but I think that /VW does a few other things too. Just for the record, I was NOT trying to use /APIC with OS2APIC.PSD.
if just a wireless driver existed :-(
You said you have an Intel device. Apparently, Intel will be the first on the list when Multimac gets around to producing a WiFi driver. Meanwhile, there are a LOT of people waiting for that (including me).