When you first installed Windows, you were given a choose to make a network connection and if I remember correctly, the default was Homegroup. So if you chose that option maybe that's why it's a apearring as if you're using a Homegroup.
I mentioned server because looking over your screenshots you identified one computer with the name server. i guess I just assumed you had a server.
On the Windows &7 machine, go to Control panel > System, click the Change Settings button at the lower right corner, click NetworkID and choose Home network and restart.
i believe if you choose the business network, you'll need an actual server to join a domain.