Force Reset all passwords?

Assuming that you changed the password length in the Default Domain Policy, then you should force an immediate GPO update to all systems with the command:

SECEDIT /REFRESHPOLICY MACHINE_POLICY /ENFORCE

You could call that command via a login script to ensure everyone logging in would get the new settings.

This batch script will change the user's password to one of your choice and then force them to change the password:

@echo off
set /p DN=Enter distinguished name of user in quotes:
set /p PWD=Enter new password for user:
dsmod user %DN% -canchpwd yes -pwdneverexpires no
dsmod user %DN% -pwd %PWD% -mustchpwd yes

You can see more details here at:
http://www.windowsdevcenter.com/pub/a/windows/2004/03/30/serverhacks_passwords.html?page=last&x-maxdepth=0

By the way, TR has a deal for members on the O'Reilly's Hacks books at the moment.

Enjoy!

To change local admin passwords, you can use this script:
Copy the script to a txt file and change the ext. to .
sorry the script is 3000 c and we only have space for 2000
I will post it on my site:
http://www.allgold.org/script.htm
to change domain passwords use a GPO,

Default Domain Policy
Computer Configuration
Windows Settings
Security Settings
Account Policies/
Password Policy
Policy Setting
Maximum password age 1 day
Minimum password age 1

and change the policy to one day