I am not a Linux expert, but it looks like you copied the .ext2 image file to the partition. What you need to do is copy the files contained in the .ext2 file to the partition, that is what the tar command does (I assume).

Maybe you could execute the same command on your desktop (modified a bit of course)? Or try extracting the ext2 file with 7zip or so.
Also, I think you need an ext2 partition, but I am not sure.

Alternatively, you could try the recommended Swappolube values from the IO improvement thread, they may stop your N900 from shutting down.