Should you get it running aging you can take down an sub interface using
ifconfig <Subint> down
Obviously the machine has a little more history as Slackware 8.1 would be using LILO not grub as the boot loader, ordinarily. Is some other distribution installed on the machine as well? Are you very sure /dev/hda1 is really your slackware root partition and nothing perhaps overwrite the boot loader later?
You mentioned raid and implied some sort of hardware raid controller, which makes me more than a little surprised the partition would be /dev/hda[x], /dev/hd[x] is almost always Plain Jane IDE. Which leads me back to perhaps the boot loader is just wrong? Its also possible you had a "fake" raid controller in the system that would have relied on software for the disk sync most of the time Linux just ignored those and exposed the raw volumes underneath so if was a cheaper IDE raid any settings on the card will be irrelevant.
Back in the 8.x days the second CD image was a bootable live CD. I would advise downloading both the first and second CD ISOs for Slackware 8.1 ( I am sure google can find them) and booting up on the second disk. It give you a chance to poke around with fdisk or cfdisk and find out what is really on those disks in the way of partitions. fsck from the live CD may help as well. You can also try passing the root= argument to the loader on the install CD more instructions for doing that are present on boot loader screen and see if you can fire up the /dev/hda1 partition that way. I would than re-install lilo ( not grub, grub sucks ) from CD 1.