You have to ssh to the server and run /usr/sbin/usermod <username> -p crypted-password

Eg :-

   $crypted_pass = crypt $password, substr(crypt(rand, "AA"), 2, 2);
   system("ssh", "-l", "root", "www.perlmonks.com", 
      "/usr/sbin/usermod '$user' -p '$crypted_pass'") == 0
      or die "...";
[download]

(Just kidding ;-)