We did that, on the mac the port is 6348 and on the PC it's 6346.

I tried to connect to the pc using both the internal IP address ([Edit]) and the external IP:6346. But none of them work.

On the pc, I tried the same thing with 6348, but it says that a firewall or a router is blocking the direct connect feature. The firewalls of both computers are disabled. Now it seems that it's really just a router problem and that it it's a pc thing because we can't connect to anyone at all with that computer and it doesn't have that little added paragraph I mentioned earlier. BTW, on the mac, in that paragraph, it says that my IP adress is the external one:6348, not the usual internal [Edit] that it shows me when I look in my system preferences.