In a nutshell. Read this:
http://plugcomputer.org/plugforum/index.php?topic=319.0The important parts are to set up your cross compiler. I used the instructions from the cd on how to build the kernel.
After that. Do this, from the above post:
1) tar jxvf u-boot-1.1.4.tar.bz2
2) mv u-boot-1.1.4 u-boot-3.4.16
3) unzip u-boot-3.4.16 (this will overwriting existing files)
4) cd u-boot-3.4.16
5) make mrproper
6) make rd88f6281Sheevaplug_config NBOOT=1 LE=1
7) make
The output should be u-boot-rd88f6281Sheevaplug_400db_nand.bin
If you are Using Ubuntu and not Fedora edit the main Makefile and change occurrences of echo -e to echo. Do this BEFORE number 6 above.