you need to be more specific.

could be a NT$ domain in which case you would use user manager for domains, or Windows 2000/2003 in which case you would use Active Directory USers and Computers.

Need more information ?

However you state you have user name and password for domain administrator, does that mean you are the admin or just have access to the account.

If so this is not a how to hack or cary out illegal activiites site, it is a professional security forum and so only legitimate requests for information will be answered, besides if you are indeed the amdinistrator then you would know how to create a user so that leads me to conculed you are not and have just come across the admin account and passowrd in which case you will be doing potential dmage to someone elses system