DirectAccess is designed so that you always get a single server environment up-and-running first before you start tinkering with arrays or load balancing. This way you can validate that all of the environmental factors are in place and working and that you can successfully build DA tunnels from your client computers before introducing any further complexity into the design. Once established, however, it is a common next step to look into turning up another new server and creating some redundancy for your new remote access solution.
While joining two similar servers together to share the load is commonly called clustering, and sometimes I hear admins refer to it as such in the DirectAccess world, load balancing DA servers together actually has nothing to do with Windows Clustering. When you install both the remote access role and the Network Load Balancing feature onto your remote access servers, you have already equipped them with...