You need to be able to Port forward you dedicated computer so others can have access. You will also need either :
1) A static IP address so your friends can find you on the internet.
2) Report to them what your current IP address each time you start to game (Via email, telephone, or other means).
3) Use a Dynamic DNS service that allows you to run a server with a Dynamic IP address.
I have used NO IP.com
to host a web site from my home computer on my cable modem. It is a free service. Another site that will be of help is Port Forward
. The will allow your computer to be accessed to from the internet.
Hope this helps, good luck.