You guys are something else. I AM a sysadmin that is encountering the same problem (except I know the current password). A google search leads me here and this is your advice? Seriously, even if you did have a root password hack, the guy would either need root permissions to do it ( e.g.: could still log in via ssh passwordless auth) or physical access to the box in which case its trivial to change, but then you incur downtime.
No wonder I rarely check techrepublic for anything other than windows desktop tips. Useless and clueless. Notice that he says after forcing a change, he can authenticate as root, but then makes him change his pw before continuing? Since it won't allow changing the pw without forcing, interactive password authentication login is not possible. If he didn't know the correct password, it wouldn't even ask him to change his password, it would say access denied.
Pay attention.
To the original poster: You didn't say what OS and version you are running or if you are using a naming service. I see you posted on other websites and got far more helpful advice (none of which were hacks) and have probably solved the problem by now. Try googling with more specifics such as the os version, etc. Try passwd -r files, try looking in the man page for passwd. Check your nsswitch.conf file, check your pam config. Check the manpage for pwconv, this might help. Run man -k passwd to see other possiblities. Good luck.