Okay. After months, I finally found time and will for another attempt on Slackware installation. Because something didn't seem right, I re-installed Slackware once again, then followed all of astrogeek's steps in post #11. LILO now shows up when I boot my laptop, but when I select Linux in the list (which is the only option since I didn't want to add Windows to it until Linux works fine), I always end up with a Kernel panic: I wish I could post the call trace here, but firstly, it won't let me scroll up to see the entire trace, secondly, often it won't even load up the entire call trace before it freezes at a blinking cursor.

What I did:
- Noted down the ID's and UUID's I needed (which were both hard drives and all three of my Linux partitions, I wrote down a Windows partition too, but it's the Recovery partition and the C: partition I would need to make bootable doesn't seem to have a partition table, at least it doesn't show up in my list).
- Modified /etc/fstab, commenting out the existing stanzas and adding new ones using the UUID's I gathered. Rebooted once, didn't find anything about UUID's in the mounting process, but moved on anyways since I don't know how I can tell it mounted by UUID's and not by /dev/sda etc.
- Created a new MBR on the first hard drive, which is my Windows hard drive.
- Made a copy of the lilo.conf, called it lilo_disk1.conf, and modified the lilo_disk1.conf to change the boot hard drive to the ID and change the root partition to the UUID.
- Tested the lilo_disk1.conf, 3 warnings but no major issues, then wrote the lilo_disk1.conf to the MBR.
- Rebooted, LILO bootloader screen showed up. Chose Linux in the list, a bit of waiting, then Kernel panic. Two more attempts, same result.

Now how do I fix this?

The much simpler way to do it is to make the Slackware drive the BIOS-preferred boot drive by setting the boot order in the BIOS. Then install Slackware on the drive, using LILO expert configuration to add Windows (primary OS) and Slackware (secondary OS) in that order to an MBR LILO install on the first (Slackware) drive. You may use whatever partitioning layout you like (just one root partition and a swap should be fine if you will never need to migrate your /home). On reboot, the Slackware/LILO drive should boot, being first in the boot order, and LILO, on its MBR, should show up.

If it does, that's good. Now select Slackware (Windows shouldn't boot at this point even though you added it to the boot list). Slackware should boot correctly. Then open the file /etc/lilo.conf and under the "other = " Windows section you should find commented-out (#) lines "map-drive = 0x81" or something like that and "to = 0x80" etc. Uncomment those four lines by removing the hashtags at the start of the line. Save the file and in a terminal type:

Reboot. Now Windows should boot as well.

Hopefully it works. If it does and you want to know how this fixed it, I'll be here. Essentially, all we're doing is letting the Slackware drive control boot-up. This is how my computer is set up and it works very well. This way you don't need to use UUIDs and you only need one LILO configuration file.

Here's my old yet reliable method of installing:

1. If I have Windows on the same disk I keep the Windows system and boot partitions. The system partition is actually the equivalent of the Linux /boot partition and is used with BitLocker and TPM. Defragment and shrink the main Windows partition. Depending on the size of your drive try to allocate at least 100GB of free space.

2. Using cfdisk for mbr+bios motherboards create a primary Linux swap partition at least 2x the size of your RAM but no larger than 8GB, and then create a Linux partition from the remaining space.

3. When you install Slackware, use only the Ext4 or JFS file systems. Due to the fact you will be dual-booting on a BIOS+MBR system, you will be installing Slackware on a single root tree. I recommend Ext4 for performance and JFS for data integrity. Do not use BtrFS, XFS, or any other file system!

4. Install Slackware as normal and have LILO run as the bootloader. Remember, if you update the kernel, rerun liloconfig, or LILO and have it automatically add everything. Do NOT let Slackware mount your Windows partition in fstab in the installation, let it automount instead from udisks after boot.

5. Reboot and you should be given the options of Windows or Linux. Enjoy.