I did this last night funnily enough using Cyberduck too, also trying Fugu as well, both work very well.

What I did was change the root password to begin with. You can do it by entering

sudo passwd root

into the terminal, and you get to change the password in the next step. Note you wont see anything when you type.

Then in Cyberduck, just enter the IP address for the N900, make sure its port 22, username is root, and the password is what you just entered. This should work!