2.4 is missing a 2.6 fix that is necessary to build CONFIG_ACPI && !CONFIG_PCI and the build fails like so: arch/i386/kernel/kernel.o(.text.init+0x3cd0): In function `disable_acpi_pci': : undefined reference to `use_acpi_pci'
fixed: http://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/test/2.4.22/20031020230720-use_acpi_pci.patch