If a customer has enabled the default Window's Administrator account, the account will be disabled after running the "Create Disk Image" using the [Prepare using Sysprep]
This is not an issue unique to DS. By default, Microsoft disables the built-in administrator account because it is a potential security hole. All DS does is supply a sysprep file to Windows 7 that returns the built-in Administrator to the default state which is 'disabled'
You can modify a sample copy which is located under \Altiris\eXpress\Deployment Server\Sysprep\standardwes7.xml You may download the updated 'unattend.xml' attached to this article. To use a custom unattend.xml, in the Distribute Disk Image task, under [Prepared using Sysprep], there is a [advanced settings], select [use the following answer file].