This is probably old news but something I just learned. I'm sure you all know the built in remote desktop in Windows defaults to port number 3389. Through a registry change you can change that port number to any port you want. Here's the registry key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations
\RDP-Tcp\PortNumber
Now in your router settings just forward the new port number to that computer and yes a router is required for this to work. You will have to specifiy the port number when you connect though. Also this is only if you need to connect to multiple computers over the internet.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations
\RDP-Tcp\PortNumber
Now in your router settings just forward the new port number to that computer and yes a router is required for this to work. You will have to specifiy the port number when you connect though. Also this is only if you need to connect to multiple computers over the internet.