That will be an issue, you may want to look at something like SplashTop or TeamViewer as it runs a client on the host.
On the Internal Network you should be able to connect just via the 192.168.1.100. On the external network you need the Public IP address of you modem (Click on Status) and then you put that IP Address in the connection string (since you are using the default port you can just use the IP Address). The Host needs to be Windows Pro, Ultimate or Enterprise to support RDP Connections.