Some technical information about the Zaurus machines from http://linuxtogo.org/gowiki/LinuxDevices
For the Zaurus a special kernel+initramfs has been developed. This special-purpose kernel is small enough to be flashed on NAND and features a frambefuffer graphical menu for the selection of the boot media containing the kernel which will be kexec'ed.
Multipartitioned cards and lot of filesystems supported. The kernels to be launched are searched in /boot of each available partition. There is a also configuration file /boot/boot.cfg allowing to pass a custom cmdline and specify the label and the icon.
How to install:
Just unpack zaurus-installer-YOURMACHINE.tar.gz on a free partition: the package contains the kexecboot-kernel and the updater.sh utility. Then proceed as usual for flashing (switch off, pull battery out, insert battery again, before inserting AC plug press OK+Power On, in the Japanese Menu select 4 and finally 3 for SD card or 4 for CF). Screenshot
For SL-5500 (collie) and optionally for other Zaurus too, flashing is possible just using the routines of the original firmware: reset the unit, Press C, and D button during restart.