Or you could uninstall dropbear and install openssh instead (sudo gainroot; apt-get install ssh) - always works for me.

Your N800 should be ping'able from a PC under normal circumstances.

The default root password on the N800 is "rootme", and user does not have a password so add a public key to ~user/.ssh/authorized_keys for user and you should be able to ssh straight in from your Linux box.