From Fedora Project Wiki

HOWTO: Sheevaplug Fedora SD card Boot

This HOWTO assumes that you have read the USB Boot HOWTO as it mainly points to the differences between USB and SD card boot.

Prerequisites

The U-Boot bootloader supplied with the Sheevaplug doesn't support booting from a SD card, but there is an experimental version that does. You can get it from Sheevaplug forums

Links

http://www.cyrius.com/debian/kirkwood/sheevaplug/unpack.html