When I modify /etc/passwd, I still can't telnet into my box.

The NSLU2 keeps multiple copies of /etc/passwd. You may also need to change the copies in /usr/local and /share/*/conf/.

 
     1: /share/hdd/conf/usr/local/passwd
        /share/hdd/conf/passwd
        /share/flash/conf/passwd
        /share/flash/conf/usr/local/passwd
     2: /share/hdd/conf/etc/passwd -> /share/hdd/conf/passwd
        /share/flash/conf/etc/passwd -> /share/hdd/conf/passwd
     3: /usr/local/etc/passwd
 

Marked with 1 are the locations you should check and edit. Marked with 2 are links only.

How to change the password from the command line.