|Knowing your public IP address isn't enough.|
To remotely connect you need to enable RDC (remote desktop connection) on the computer you wish to connect to.
If you have a SOHO Router, you have to create a port forward in the router to send the incoming RDP session to the (internal) IP address of the computer you wish to connect to.
If you don't have a SOHO Router, then you'll have to allow that RDP port (typically 3389) through the built in firewall of the client.
Assuming you have a router:
1) Enable RDC on the client you wish to connect to (No, don't ask us how, use your imagination. That info is available in the Windows Help files as well as on the web)
2) Open a command prompt window on the client you wish to connect to (Start >> Run >> type in cmd and hit Enter) and do the ipconfig /all command to find out your clients internal IP address. Write that down.
3) Connect to your router's management interface through your web browser. Find the "port forward" section and create one that will send requests on port 3389 (RDP) to the internal IP of the client you want to connect to.
4) Go to what's my ip and find out your external (public) IP address. This is what you will connect to through RDC on the remote computer.