Another thing to try
I've found that using the pci=noacpi was not enought. I had to use acpi=off as the parameter to the linux kernel. It does make a difference. append="hdd=ide-scsi acpi=off"
I also have to set DMA as on for the cd drives (in my rc.local file on boot). The command is "/sbin/hdparm -d1 /dev/hdd" to set DMA as on. 2.4.21 seems to not want to set the DMA on for cd drives. You can issue the hdparm command from the command line too.
As a side note, in 2.4.22-preX I've had to remove ACPI from the kernel all together to get nvnet and audio to work stabilly.