you need to route any traffic on port 21 to your computer so this needs to be configured on the router and you probably also have firewalls in your way too.
If you do have access to the router then it is a simple job, but without unfortunately it cannot be done.
if you have an extra computer, look into www.clarkconnect.com . i am using this as a web server/ftp server. it works great. and it's free. it's a version of linux that runs like a gateway, with a bandwidth controller, port forwarding, etc. all in an easy to use interface. try it out.
