Answer
If NS has imported Sites and Subnets from an Active Directory implementation and it is necessary delete the items the default method within NS is to use the Site Maintenance delete button, "X", in order to individually delete each site and subnet. The problem with this if you have more then 100 sites or subnets the process of manually deleting each one becomes time consuming. The easiest way to delete multiple sites and subnets is within the actual Altiris Sites and Subnets Resource Type. To access these resource types navigate to the following location and select either “Site” or “Subnet”:

Resources Tab\Resource Management\Resources\Other Resources

Within the Resource Type select the Sites or Subnets you wish to delete from the DB, right-click the selected items and choose delete. This process will then properly go through the CMDB and delete the selected items from NS.