I think what WarheadSE and the others mean is that you should download the Arch Linux ARM rootfs from
here (check it against the md5sum 9e71b0c31ddba5d982f12b2d24f72ad8, but this is valid as of two days ago, presumably still valid right now - WarheadSE can give you a better idea on this then I can). Preferably download it using wget and not using your browser.
Then do the steps that jmandawg mentioned (though incidentally as far as I know you would be downloading the rootfs and not the kernel).
Make sure you do all of them as root, and you need to do it on another linux machine. If you are not familiar with command line commands at all, google for each of the commands so you have a better idea of what they do. What he's suggesting, in terms of actions, is:
1. What he said
2. Use fdisk to create one partition on the drive (presumably you already know how to do this since you had used fdisk)
3. Use mkfs.ext3 <new partition - e.g. /dev/sdb1> to create an ext3 file system on that partition (double check that you are giving it the correct partition, it will wipe whatever partition is specified)
4. Use tar to extract the file I have linked above to the pen drive partition, after you have run mkfs and have mounted the new partition somewhere (tar -xvzf <downloaded filename>, run from the directory where you have mounted the partition, should do the trick)
5. Type "sync", let it finish; then unmount the drive and AFTER it has been unmounted unplug it from the computer
6. Plug it into the Pogoplug and start the Pogoplug
Incidentally absolutely DO NOT run the oxnas-install script again on your plug at any point - someone else on the forum bricked their plug by doing that.