if you're using the method in the DaOne sticky (with make and make install), you should ADD the text after the text you already have (and change your root partition to the right one, as in the directions), i.e.:
image = /boot/vmlinuz.old
root = /dev/hda3
label = slack.old
read-only
~~~~~~~~~~~~~~~~~~
>edit for your proofread:
to clarify, you should KEEP the text you already have in your lilo.conf, and you should ADD the text above TO the lilo.conf file. so when you're all done, it should look something like this, with both parts in the lilo.conf file:
image = /boot/vmlinuz
root = /dev/hda3
label = linux
read-only
image = /boot/vmlinuz.old
root = /dev/hda3
label = slack.old
read-only
if anything about that's not clear, just ask again.