Go to the start screen and type in "Remote Desktop". Click the icon that pops up. Then, put in your public IP (which can be found by typing in "What is my IP" into Google from your desktop). It should come up asking for a username and password.
A few things to check out: If you have a router, make sure port forwarding is set up for port 3389 to your computer's private IP address and make sure your desktop's firewall isn't blocking svchost.exe.
Thank you - I tried most of what you suggested and I still can't get this to work. I found the public IP of my desktop, I put that into the 'PC name' box at the bottom of the screen on the Windows RT Remote Desktop app. It gave me the message:
"Can't connect to the remote PC.
Make sure the PC is turned on and connected to the network, and that remote access is enabled."
I even turned my firewall off for a few moments to try again and there was nothing.
Do I have to be on the same network for remote access to work? The way I am running now is my desktop is wired in and I have a wireless USB stick feeding internet to my devices using Connectify. I think that technically they are on different networks because of this. At home my desktop is on the same wireless network as my tablet - would that work better?