By default, as was with Vista, the local Administrator account in windows 7 is disabled. If you are deploying Windows 7 across a number of clients on a network etc. you may find the need to enable this account for future trouble shooting client machines. Also remember, even if you enable the Administrator account, and then run Sysprep, the sysprep process disables the Administrator account.
By far the easiest way to enable the Administrator account on client machines in a domain is to use Group Policy, here is how you achieve this.
I am assuming you have the basic understandings of applying/creating Group policy settings on a Windows Domain, if not, leave a comment and i will see how i can help further.

Go ahead and open “Group Policy Management”, for testing purposes, it may be worth creating a new policy on a test OU, and placing some test client accounts within that OU. So Right click your OU and select “Create a GPO in this domain, and Link it here”. The new GPO pox will prompt you for a Name, so go ahead and give it a meaningful Name, and click OK.