Customize password complexity requirements

Normally you would use Group Policy to accomplish this.

Here is some info for you...

from: Microsoft

1.Open Active Directory Users and Computers.

2.In the console tree, right-click the domain or organizational unit that you want to set Group Policy for.

3.Click Properties, and then click the Group Policy tab.

4.Click an entry in Group Policy Object Links to select an existing Group Policy object (GPO), and then click Edit. You can also click New to create a new GPO, and then click Edit.

5.In the console tree, click Password Policy (Group Policy Object [computer name] Policy/Computer Configuration/Windows Settings/Security Settings/Account Policies/Password Policy)

6.In the details pane, right-click the policy setting that you want, and then click Properties.

7.If you are defining this policy setting for the first time, select the Define this policy setting check box.

8.Select the options that you want, and then click OK.

You will want to set: Password must meet complexity requirements and Minimum password length

And for a product recommendation:
http://anixis.com/products/ppe/ can do all that and much more. Simple, easy to learn, (for me) so far bug free and worth the money.