Default debian Lenny installs set your editor as nano. Say you edit $USER/.ssh/authorized_keys2 and paste in your pub key, what do you get when you try to log in?

sshd error: buffer_get_ret: trying to get more bytes 4 than in buffer 0

You needed to use 'nano -w' (or better yet, vim) to make sure that the public key entry in USER/.ssh/authorized_keys2 is all on one line. Thanks to kaliphonia whose relative google rank for me is link #8.