Slackware now has support for the SheevaPlug, and is available for testing!
I've only just finished adding the support, and whilst it works for me on my two SheevaPlugs - installing onto a 16GB USB stick, and a USB hard disc - please consider the SheevaPlug support (Kernel and installer) as an alpha release. The rest of the distribution (minus the Kirkwood Kernel & installer) is stable -- currently at release candidate 4, scheduled for a release in a couple of weeks.
This version of Slackware uses the 'old abi' - work on an EABI port will begin soon.
Please see the installation document:http://ftp://ftp.armedslack.org/armedslack/armedslack-current/SHEEVAPLUG_INSTALL.TXT
The changelog, which includes details of the updates, is here:http://ftp://ftp.armedslack.org/armedslack/armedslack-current/ChangeLog.txt
In the installation document, I post the instructions for upgrading U-Boot on the SheevaPlug. This is the only way I found to get console output of the booting Kernel - unfortunately I didn't take note of the environment settings before I upgraded my device; so I don't know what needs to be changed -- I suspect upgrading U-Boot is not necessary. Please let me know if anybody figures out what change needs to be made.
I'm on holiday next week, so I'll reply to any queries when I'm back, but I'm pretty confident that you should be able to follow the instructions at the document URL above, and get Slackware installed onto your SP.
Thanks & enjoy!