You guys are forgetting something very important too -> the router, which acts like a hardware firewall as well. You should go and port-forward the ports 20 and 21 on your router/modem.
I, too, am using IIS FTP server and had no problems whatsoever setting it up, which was quite easy.
If you have another computer around, you can try to connect through your local network and see if it works. To know the address of your computer on the local network and not the public IP, just use the ipconfig command in the cmd window like shown below.
Sorry for the french console. And yes, I did remove some information.