How To Determine If Your Computer Is Being Assigned The External IP Address ?

For Windows 2000, XP, and 2003
1. Click Start
2. Click Run
3. Type in cmd and hit ok
4. Type ipconfig and hit enter

For Vista
1. Click Start
2. Click All Programs expand the Accessories menu
3. In the Accessories menu, Right Click Command Prompt and choose Run as administrator
4. Type ipconfig hit enter

Results
If you see an IP that resembles 192.168.n.n then this is an internal IP address assigned by a router. So your router is getting your external IP address. If the IP displayed in the command prompt window matches the one shown on What Is My IP then your computer is being assigned your external IP.