Mike:
You will be using the "Virtual Server" capabilities of your router. So, with this in mind, do the following...
1) Log into the router...
2) Go to the Port Mapping option of the router (Configuration/Port Mapping). This is on page 120 of the manual.
3) You will enter a name for the application ("MineCraft" will do)...
4) Set the protocol to TCP
5) The External Port Number is 25565
6) Set the Internal IP Address to your server (192.168.xx.xx)
7) Set Internal Port to 25565
8) Click "Add"
This will add a line into the router table that directs all access to port 25565 to the machine specified in the IP address...
In order to play, no DYNDNS or any other BS lame crap like that needs to be had... just figure out what the external IP adddress is via "Myipaddress.org"
http://www.myipaddress.com/show-my-ip-address/ and e-mail that address to your friends... if you reboot the router, then you will need to re-send the IP address around again.
If you have a fixed IP, then you will not have to worry about any dynamic aspects....
OIC!
<LATE EDIT: Make sure your server accepts the port you specify... if you are in Windows, it will be under the Control Panale/Security/Firewall/Allowed Programs tab. Linux access varies by distro, so if you are using Linux, let me know which type and version...>
<Even Later Edit Based on other peoples postings....: If you want some security tips in relation to private servers, give me a shout... some people are correct in that port trolling can be a problem (I do it often)... and some crackers (not hackers) can get in, but to be honest, the number of people who ACTUALLY know how to do this is limited, as most are just "script kiddies" claiming to /b/L33t....>