To use the "Active Directory Installation Wizard" to remove Active Directory, you must know the password to assign to the local Administrator account of the server after Active Directory is removed. To perform this procedure, you must be a member of the Domain Admins group.
To uninstall Active Directory:
-Click Start, click Run, type dcpromo and then click OK.
-The Active Directory Installation Wizard appears. Click Next at the Welcome screen.
-You have an option to select This server is the last domain controller in the domain. If you select this option, the wizard attempts to remove the domain from the forest. Do not select this option. Click Next.
-At the Administrative Password screen, enter and confirm the password that you want to assign to the local Administrator account after Active Directory is removed. Click Next.
-At the Summary screen, verify that the information is correct and then click Next to proceed with the removal.
-The wizard proceeds to remove Active Directory. After it finishes, the wizard displays a completion screen. Click Finish to close the wizard.
-Click Restart to restart the domain controller.
The above is for Windows 2003 Server
. Is that what you guys are using?
For Windows 2000
use the guide here: