How do I install the ARM version of Slackware Linux on the Raspberry Pi?
I haven't done this personally, but I'd start with something like this:
It seems like fatdog.eu has all the information you'll need to get slackware running on the rpi.
Ejoso's tip was great, but fatdog.eu has been offline for some time. Another site with nicely written step-by-step instructions can be found here:
http://sarpi.co.uk is not another site. It's the same people from FatDog.eu who are running it. But nobody knows when FatDog.eu will be back online so they hosted it elsewhere.
This is new URL for the SARPi Project.