Friends get "Can't Reach Server" Error; Port forwarding?

[nalexander50]

I recently set up a sever at my buddy's house with their WAN. The server ran just fine and we played quite a bit. I came home today and tried to play without thinking about it and realized that I was still trying to connect with an IP Address that didn't belong to me. I changed the server IP to MY IP address without thinking about it, but now my buddy can't connect because that's my private address. I understand the problem perfectly. I just need help fixing it! I have dabbled around countless forums and sights searching for Port Forwarding help before posting here.

I am running Mountain Lion on a Mac and using a Belkin N600 Router. Under my router settings there is not a dedicated Port Forwarding tab, but under Firewall there is the Virtual Servers tab which is Belkin's version of Port Forwarding. I have a Description, Inbound Port, Type (TCP / UDP), Private IP Address, and Private Port. I know that Minecraft uses the 25565 port; but that is about all I know. Can I get some help here? Furthermore, I am using a dynamic IP - will that cause problems? If so, how can I fix that?

If any additional information is needed I will be perfectly willing to share.

I'd ask that we not bash the new kid who is just learning his way around Tekkit. I apologize if I posted in the wrong place or such. I would just like to have fun with Tekkit, and I can't quite do that unless my question is answered. So let's all be good mannered if possible!