You can also use the built-in PPTP VPN. This will create a secure tunnel to the SME, and give your remote PC a LAN IP behind the SME. You will have the same access you would if the PC were physically on the SME's LAN.
Just enable at least one VPN connection in Server Manager, and set up a PPTP connection from the remote PC. In Windows, just make sure you have DUN 1.4 and VPN is installed, and add a new DUN entry for it, specifying your SME's external IP or domain name.