RDP only Operating System
I am looking for an operating system where the login screen asks for a username and password for an rdp login prompt. I want an administrator to also be able to login to change the i.p. address for the server that hosts the accounts. Any suggestions?
Take a look at the xrdp package. You can install it on most Linux distros. Should be in the distros' repositories. There's a pretty good tutorial here titled: Connect to Ubuntu 12.04 (Precise Pangolin) via Windows Remote Desktop.
Xrdp provides a RDP layer so that you can use the RDP client that's available on Windows and/or the XFreeRDP client available to Unix. Locally on the host, xrdp is really just a wrapper around VNC, however it keeps the VNC connection so that it's all self contained on the host via losthost only.