1. Run gpmc.msc (Group Policy Management)
2. Expand Forest
3. Expand Domains
4. Expand your Domain
5. Expand Group Policy Objects
6. Right-click Default Domain Policy (or your desired policy object) and choose Edit
7. Select the Settings tab
8. Then browse to Computer Configurations → Policies → Windows Settings → Security Settings → Account Policies → Password Policy
9. Edit the settings or disable Password Complexity

Here is a quick and simple function which authenticates a user to AD at the PowerShell command line:

Function Test-ADAuthentication {
    param($username,$password)
    (new-object directoryservices.directoryentry "",$username,$password).psbase.name -ne $null
}

PS C:\> Test-ADAuthentication "dom\myusername" "mypassword"
True

http://www.wisesoft.co.uk/articles/bulk_ad_users_beta_testing.aspx

http://www.wisesoft.co.uk/articles/password_control_2.5_betatesting.aspx

Forums: http://www.wisesoft.co.uk/forum/forum1-password-control.aspx

Tools from WiseSoft help when manipulating multiple users, as during a new installation or cutover.