To make it so that you don't have to type that crap in everytime you put it into the lilo.conf file. Then re-run lilo.
Check out "append" in the "man lilo.conf" file. The config file is /etc/lilo.conf
If you have any initrd lines, be sure to leave those in there. Also you can multiple entries so that you can simply have a unmodified entry with a different label (say linux.backup?) and use that if your "append" changes made it unbootable.
image=/boot/vmlinuz
root="/dev/hda3"
append="acpi=off apm=off noapic"
label = Linux
read-only
image=/boot/vmlinuz
root="/dev/hda3"
label = Linux.orig
read-only
something like that.
Also for lilo you need to re-run the "lilo" command to make it load up into the bootloader. Be sure to save a backup config so that if you mess up a bunch of lines and accidently saved it then you can go back and simply copy the original version back into place.
Also check out making your own kernel. You can edit out any acpi or power managemernt support. Also this stuff has improved quite a bit since the latest version of slackware was released and may have the problem fixed.
Check out
the linux documentation project, and check out this
kernel rebuild guide
Basicly you go and make a backup to your /boot/vmlinuz to something like /boot/vmlinuz.original and make a entry for it in /etc/lilo.conf so you always have something you can use. Then you go to ftp.kernel.org and find and download the latest 2.4 series kernel (2.4.27 I think), copy the tarball to your /usr/src directory. Then untar it (tar zxfv kenrel-blahblahblah.tar.gz). Change into the new directory, run some make commands: "make mrproper" to get the sources "installed", "make menuconfig" to get the console menu dialog for configuring the kernel, then "make dep", followed by "make modules", "make modules_install", and finally "make install". Go look at your new kernel image, make sure that /etc/lilo.conf is all correct and has a entry for it, rerun lilo and you should be ready to reboot using it.
Hopefully you did a "install everything" or whatnot when you installed slackware otherwise you may have to install ncurses developement stuff to get the menuconfig working. I've ran into that a couple times on fresh installs, also there is like xconfig for configuring using X windows dialog.