If you don't know of any settings/configs then you've probably
not customized anything yet, so don't be concerned.
I'm not sure if LiLO will overwrite GrUB or not. When I moved
from Debian to Slackware I had it on a separate drive and/or
partition and formatted before installing. That's probably not
necessary. When you install Slackware you can change your
partitions and then during setup you can either format your
partitions, or skip the formatting.
How is your current system laid out?
# fdisk -l (lower case L)
$ df -h
$ /sbin/lspci
I'd save the output of those commands so that when you're
installing Slackware, and then later setting it up, you'll have
them for reference.
I believe that if you choose to put LiLO in the MBR, it will
write over GrUB, but I'm not sure. You might want to search
LQ and also
Google <Linux> to find out.
On the Slackware CD1 there is a file titled Slackware-HOWTO
and it will give you some good installation instructions. If you
need to, print it out. I would make one change from those
and that is to use cfdisk rather than fdisk to change any of
your existing partitions.