i've gone through similar issues as to what you're describing.
here's the uboot config from
your install link:
setenv bootargs_console console=ttyS0,115200
setenv bootargs_root 'root=/dev/sda2 rootdelay=10'
setenv bootcmd_usb 'usb start; ext2load usb 0:1 0x0800000 /
uInitrd; ext2load usb 0:1 0x400000 /uImage'
setenv bootcmd 'setenv bootargs $(bootargs_console) $(bootargs_root); run bootcmd_usb; bootm 0x400000 0x0800000'
if you notice, the sheeva.with-linux.com kernels only have a uImage, and not a uInitrd, so the above boot configs will not work properly.
using
this link as reference, i came upon the following:
setenv bootargs_console console=ttyS0,115200
setenv bootargs_root 'rw root=/dev/mmcblk0p1 rootdelay=10 rootfstype=ext2'
setenv bootcmd_mmc 'mmcinit; ext2load mmc 0 0x800000 /boot/uImage-2.6.30-sheevaplug'
setenv bootcmd 'setenv bootargs $(bootargs_console) $(bootargs_root); run bootcmd_mmc; bootm 0x0800000'
i modified this for my config on my sdcard and it works. so, in your situation, if you have sda1 as /boot and sda2 as /, i would try something like this:
setenv bootargs_console console=ttyS0,115200
setenv bootargs_root 'root=/dev/sda2 rootdelay=10'
setenv bootcmd_usb 'usb start; ext2load usb 0:1 0x0800000 /uImage'
setenv bootcmd 'setenv bootargs $(bootargs_console) $(bootargs_root); run bootcmd_usb; bootm 0x0800000'