The 'non-developer' documentation that everyone is asking for ;-)
In order to keep these instructions simple, I'm going to make some assumptions:
You've already got linux running on your desktop PC (I've not tried these instructions in VMWare or VirtualBox, but using a LiveCD should work fine)
You've got sudo working (allowing you to run commands as root)
Your USB flash drive (or USB hard-drive) is at least 1GB and appears on your linux system as /dev/sdd (modify the instructions below as appropriate for different drive letters)
You've made a backup of any important content on your USB drive (cos it's gonna be wiped)
You're using a 1MB-flash bifferboard, and you're using Ethernet flashing (and you've not disabled your bifferboard's network console in biffboot)
Update: if you're using one of the newer 8MB-flash bifferboards, simply use bb_eth_upload8.py instead in step 18 below. Everything else should work the same.
You don't blame me if everything goes horribly wrong!
Step by step instructions
Create a temp directory, and change into it: cd $(mktemp -d)
Download the tarball: wget http://downloads.sourceforge.net/project/bifferboard/slack13-rootfs-9.txz?use_mirror=mesh
If necessary, rename or decompress the tarball - as I'm on Ubuntu I renamed the .txz to .tar.xz: mv slack13-rootfs-9.txz slack13-rootfs-9.tar.xz
Plug in your USB flash drive
Run dmesg to see what 'letter' it appeared as - for me it's /dev/sdd
Unmount any auto-mounted partitions: sudo umount /dev/sdd*
Use fdisk (or gparted if you prefer a graphical tool) to delete any existing partitions: sudo fdisk /dev/sdd
Create an ext3 root partition (seems Biff's current slackware kernel doesn't support ext2!) and a swap partition - my USB drive is 2GB, so I allocated 1.5GB for /dev/sdd1 as ext3 and the remainder for /dev/sdd2 as swap.
Format the root partition: sudo mkfs.ext3 /dev/sdd1
Intialize the swap partition: sudo mkswap /dev/sdd2
Create a new directory: mkdir mnt
Mount the root directory here: sudo mount /dev/sdd1 mnt
Change into your mounted root directory: cd mnt
If you now run 'ls' you should see just a directory called "lost+found" (which can be ignored)
Extract the tarball here (see Step 3 regarding filenames): sudo tar -xvf ../slack13-rootfs-9.tar.xz
Change into the boot directory: cd boot
Connect your bifferboard to your network, but don't connect power yet
Flash the kernel to your bifferboard using the appropriate upload script: sudo python bb_eth_upload.py eth0 6a:b3:f6:00:1d:58 bzImage (you'll need to change the MAC address for the one on your bifferboard, and then plug in power to the bifferboard when the script tells you)
Hopefully it'll all go okay, but I've had instances in the past where it doesn't work first time. If this happens to you, unplug your bifferboard from the power and repeat the previous step.
Change directory out of the root partition: cd ../..
Make sure the disk buffers get flushed (which may take a while): sync
Unmount the root partition: sudo umount mnt
Wait for any lights on your USB drive to stop flashing, then unplug it
Unplug power from your bifferboard
Plug your USB drive into your bifferboard
Plug power into your bifferboard
Wait a minute or so for bifferboard to boot up
Follow the instructions on the main Slackware page for connecting to your bifferboard with telnet. If they don't work try checking your router's dhcp logs to see what IP address got assigned to your bifferboard, or you can instead connect using the serial console
That's it! You're now running a fully functional slackware installation on your tiny little bifferboard. See the Slackware page for details on installing extra packages with slapt-get
If you want you can now delete the temp directory you created in Step 1.
If you have an ext2 filesystem that you want to use with this setup, convert it to ext3 as follows:
* unmount the partition
* tune2fs -j [partition]
* edit /etc/fstab, and change ext2 to ext3 for this partition
* mount the partition