Remote Desktop (RDP) is the fancy name for logging in remotely.
By two instances I mean you have Windows Server instance 1 that has Active Directory, DNS, DHCP, file shares and Windows Server instance 2 that has Remote Desktop Services for your remote users to log on to and be presented with a desktop. This second instance is where you'd install your vendors program. Think of instance 2 as a glorified PC that supports N number of simultaneous remote logons by your users and think of instance 1 as providing the basic infrastructure to support the computing environment.
I used the word instance because instead of buying multiple physical servers, some people buy hardware that's a little more robust and install a virtualization layer like Hyper V or ESXi and then install Virtual Machines on top of the virtualization layer.
Last edited by vr; January 12th, 2013 at 11:11 PM.