Well, people on the internet are going to connect to you using your WAN IP address. You can find this by going to
whatismyip.com. Then, on your 'router,' you'll need to forward TCP port 21 to your FTP server's LAN ip address (192.168.0.x). You can find this by running 'ipconfig' from the command line on a box running the NT kernel, or 'winipconfig' on a box running then 9x kernel. (There should be some page for port forwarding or virtual servers in your 'router' configuration page.)