The messages echoed during your 'net install' seem to elude to the absence of both a kernel ("there is no kernel to install - click continue") and associated modules ("Lack of kernel module - choose to continue without those").
It seems you will need to install them independent of the net install.
Assuming the net install process got the SD card prepared for installation, i.e. partitioned and formated ( there should be two partitions, one ext2 and the second an ext3 ); you can check the partition table by running
You should see two partitions on the sd card, something like:
179 1 3928 mmcblk0p1
179 2 3868320 mmcblk0p2
If one or both of these device nodes dont exist, you will need to make them and format them.
If they both exist, and are mounted, they should have populated file systems under them, i.e. there should be a bunch of directories and other file objects in them; if this is the case, you can copy the modules and kernel image to them and you should be good to go, however, if they are not mounted you will need to mount them both to copy the needed files to them.
If you dont already have the kernel and modules on a USB stick, either manually select and download the kernel image and associated modules that you want, or grab the installer package (sheevaplug-installer-v1.0.tar.gz) @ http://www.plugcomputer.org/index.php/us/resources/downloads?func=select&id=5
and uncompress it somewhere on your PC and then copy all the files from the 'installer' directory to a USB stick/thumb drive.
...now you can put the thumb drive in the Sheeva Plug and mount it.
As mentioned above, if the two partitions on the SD card arent mounted, you need to mount them and copy the modules and kernel files to them, for example, mount partition 2 ( mmcblk0p2 ) and copy the modules file into it ( if there isnt already a full root filesystem on this partition, ie the directories etc, bin, usr, var, etcetera, then you need to also copy the rootfs file to this partition and unpack it):
mount /dev/mmcblk0p2 /mnt ( assuming you didnt already mount the USB thumb drive at /mnt, but at somewhere else, like /media)
cp /media/rootfs*.tgz /mnt
cp /media/modules*.tgz /mnt
Now cd to /mnt and unpack both files
Now unmount partition two of the sd card and mount partition one in its place:
mount /dev/mmcblk0p1 /mnt
Copy the kernel image to partition 1:
cp /media/uImage /mnt
...reboot and you should be ok, assuming all that was missing was the modules and kernel image :/