Background:
Currently running RH 8.0 with the grub boot loader:
hda1: boot
hda2: RH8
hda3: swap
hda4: slack10

Attempting to run slack 10.0. The installation process went fine. Didn't configure lilo because I had grub.

menu.lst:
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Linux (2.4.18-14)
root (hd0,0)
kernel /vmlinuz-2.4.18-14 ro root=LABEL=/ hdd=ide-scsi
initrd /initrd-2.4.18-14.img
title Slackware 2.4.26
root (hd0,3)
kernel /boot/vmlinuz-ide-2.4.26 ro root=/dev/hda4/ hdd=ide-scsi

Scenario:
It finds the kernel just fine. When the kernel is loading it lists all of the partitions. But then that dirty [explitive deleted] freezes up with: kernel panic: unable to mount rfs 03:00

I looked at the grub doc and couldn't find any more direction that what I already thought I knew. What have I missed/overlooked/frustrated you with my blindness?

Thanks in advance

First the error hints as to where the problem lies.

"unable to mount rfs 03:00".

rfs stands for Root File System. So it's unable to load Slackware's root. Looking at your config file above, notice the
First you're telling it Slackware's root is at /dev/hda3, then you're appending the kernel and telling it it's /dev/hda4/. Anyway, you shouldn't need the "root=/dev/hda4/" at all. But if you were to leave it, change it to "root=/dev/hda3".

Did you share /boot between RH and Slackware ?
if yes, try :

root (hd0,0)
kernel /vmlinuz-ide-2.4.26 ro root=/dev/hda4 hdd=ide-scsi

root (hd0,3) is /dev/hda4

grub starts numbering at 0

Its gotta be something else

I would have to agree. Grub's parition and harddrive designation is based on the BSD system which starts at 0, unlike linux which starts at 1.

The boot partition (hda1) is only for RH. Within the slack partition (hda4) there is a subdirectory: /boot, where its kernel is located.

Would it make any difference if I did share the boot partition (hda1) between both distrobutions? In the back of my head I thought they had to be separate, but I don't know why I thought that.

I didn't mention it before, but to eliminate the question: I can mount hda4, and have looked at the directory structure. So it leads me to believe its something contained within the kernel commands. But I have no idea what. I've very seldom played with kernels. The cd boot disk loaded just fine, and towards the end of the installation asked me what kernel I wanted to copy over. I told it bare.i because I figured if I needed to mess with kernel settings I'd rather start from scratch.

Hints? Allegations?

on a side note: In going thru the grub info file I couldn't find out why 'ro' is included on that line. And is 'root=...' truely optional?

Yeah, my bad it is /dev/hda4 but not "/dev/hda4/" as you have it. There is no such thing as /dev/hda4/

You are so right! I was so blind. I over looked that little typo. I fixed it and it came out just fine. I just had a completely successful Slack 10 boot. Thanks.

Good job noticing that, DaHammer. This shows that many eyes are a good thing! chrisidaho, glad you got it to boot. Now you can play with Slack! Be careful; you may end up liking it a lot!

Glad you got it going. It's usually the little things that produce the biggest headaches.