Ok guys, I've done, and re-done everything suggested here, but when I come to connect via SSH I just get a "Host Unreachable" error.

Checklist on N900:
1. Installed SSH server and Client
2. did what ever this means:

"mkdir /media/n900
chown <username> /media/n900
sshfs root@n900.host.or.ip:/home/user /media/n900 -o allow_other"

3. did "ifup usb0"

Checklist in Ubuntu
1. apt-get install openssh-server - done
2. modified /etc/network/interfaces file to add
"iface usb0 inet static
address 192.168.2.14
netmask 255.255.255.0
broadcast 192.168.2.255"
3. did "ifup usb0"

Still no joy.