Just copy the 3 files from slackware-10.0/kernels/bareacpi.i into /boot
cp bzImage /boot/vmlinuz-bareacpi-2.4.26
cp config /boot/config-bareacpi-2.4.26
cp System.map /boot/System.map-bareacpi-2.4.26
Then add an entry for vmlinuz-bareacpi-2.4.26 to your lilo.conf and run lilo.
If you can boot the new kernel with no problems (which would only be an error on your part as the kernels are the same apart from the acpi support) then you can delete your old *-ide-2.4.26 files and redirect the symlinks (vmlinuz etc) to point at your new kernel, config and map files and change your lilo.conf to reflect these changes.
Of course you could just make a bootdisk, copy the three new files over the *-ide-2.4.26 files, run lilo to check it's output for errors and reboot.
Oh and remember to add acpi=on to the kernel parameters in lilo.conf