Actually, port forwarding doesn't have anything to do with firewalls. It's so the router knows which computer to send incoming connections to.
Example:
Computer 1 <---
Computer 2 <--- Router <--- Modem <--- Internet <--- Client
Computer 3 <---
The IP just gets you to the router. From there, you have to forward the port to the appropriate computer, so the router knows if you want to connect to computer 1, 2, or 3.
Firewalls simply filter/block certain traffic (which can also cause problems, so you need to make sure that port is open on your firewall as well, if you have one).
RaiN: Part of the problem is that you're telling your friend to connect to what looks like your LAN IP address. 192.* is usually LAN IP's. Unless he's wired directly into your router, he won't be able to connect with that IP. He needs your external IP (you can get that from ipchicken.com or a number of other places that will display your IP address).