I tryed to play via TCP/IP with my friend but I didnt know with port to use so he wasnt able to connect. Then we tried to use Tunngle but we can see each other in a LAN-Game. How could we play together now?

Ah yes!
I remember when I used to play this online that connecting was a bit of a bitch to get working, though alas recently I have connected to another player via lan....

Its most probably a firewall issue. Make sure it has access through your firewall and iirc, you have to type in the ip address, not 100% though its been a long time.