I use a few methods. Whatever works best for you will vary.
I have cable on a dynamic IP and my router is a Lynksys. You need to assign a static IP to your NIC connecting to the router. The range will vary depending on the model. Read your manual or go to the manufacturer's website to get that info.
Configure the router to use DHCP for obtaining an external (WAN) IP address. This allows the router to update itself when your ISP decides to change things around. Setup the allowed connections and security settings to reflect your LAN. I'd recommend using the info from your mac address instead of the ip address of your NICs. You can get this info by typing ipconfig /all from a command line.
The Linksys I have supports
DynDNS host IP updates so I setup a free acount and Dynamic DNS Host Services. Next, I configured my router to use those credentials to update the DDNS entries from the router config screen. Every time my ISP changes my external (WAN) IP, my router gets updated and so does DynDns. So now I have a simulated static IP linked to a host domain that stays the same and ends up at my router's front door.
-=The good part-=Configure the router to forward incoming connections to the appropriate port on the appropriate computer connected to the router, known as port forwarding for obvious reasons.
For example HFS uses port 80 by default. Your HFS is running on say 192.168.1.4. Anytime the router recieves a request for HFS, it has to get it to 192.168.1.4:80. In the port forwarding setup screen, you would add the application name (HFS.exe), the incoming port (80), and the IP to forward to (192.168.1.4). You're done. Test it out by trying to access HFS from a web browser using the WAN address that your ISP gives you. followed by a colon : and the port you're using, 80 or some other non-standard port. If the screen comes up, you're done. If not, you can check your firewall to see where the connection is going by looking at the browser name in the firewall and seeing what ip and port it is trying to connect to.
I also use a method of UPnP forwading so I can run HFS on both the standard port 80 and a non-standard port. I setup HFS to run on a non-standard port and in UPnP set the HTTP port (80) to forward to my non-standard port to the correct IP address. What this means is users can access HFS from both port 80 and the non-standard port when trying to connect. You may or may not want to do this depending on your needs. The port forwarding method is quick and easy to setup and works fine.
What you end up with in the end is your own domain,
http://www.yourdomain.com, and an http server getting any external requests routed to HFS. The benefit of running HFS on a non-standard port is you can have a webpage point to yourdomain.com:12345 (or whatever) and then the HFS screen will come up. Or embed it in a frame... or make a flash app for your server... or...
