at 1st: sorry for my bad english :-)

to be root you must in file /etc/ssh/sshd_config the entry
PermitRootLogin no change to PermitRootLogin yes

thats the things i´ve done to go root like n900:

1.) activate developer-mode in phone -> settings -> security
2.) login in terminal as user: ´devel-su´, Password= ´rootme´
3.) keep own user-password: ´passwd user´
4.) open winscp with ´user´ and your own user-password
5.) in winscp open terminal (STRG/CTR+T) and type ´cp /etc/ssh/sshd_config /home/user/´
6.) now you can in change and save the file
7.) take N9 in your hand and open terminal -> ´devel-su´, Password= ´rootme´ and type ´cp /home/user/sshd_config /etc/ssh/sshd_config´
8.) then type ´pkill -o sshd´ or just reboot, and you should be have full root-privileges and you can login as root.

hope this help you.