I don't know about that example but three years ago I worked on a multiplayer shooter (/ template) for fun and I'm positive that this build here used to work: http://www.superku.de/sk_mp_test.zip If it does not work the problem indeed should be the port forwarding.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual