[Zaramoth]

Alright, I will try to help as best I can. If you have done some of these just ignore them.

Step 1: make sure both games have the same version. Since you didn't get a version mismatch so far so good.
Step 2: Make sure all the firewalls and etc. are disabled! *on both computers*. I know you said you did this but make sure they done on both.
Also make sure the Windows Firewall is disabled and/or DS2 is added to the exceptions list on both computers.

Step 3: Are both your computers hooked up to the router all the time or just for DS2? When you hook in a new computer sometimes resetting the router might help also resetting the cable modem.

Step 4: Make sure you router is up to date with the last firmware version. Also try fiddling with one computer at a time, can each computer get on the internet. It may be a router problem not the game.

Step 5: Make sure all the settings on the game is correct. This may sound silly but make sure people can join mid game. Make sure your parties work together. Like does one game have 2 characters and you are only allowing it to play with 1 character each. Try starting new characters for both and see where that goes.

Step 6: ok this is even sillier, but make sure no MODS are being run on either computer. It won't work if one game has mods and one doesn't.

Step 7: Have patience? This may be even worse than before but the second player can't start loading the game until the first player is in the game. Give it at least 5 mins minimum. Once player one is in the game player 2 should start loading.

Thats all I got so far. Consult DS2 Troubleshooting for more help.

Let me know how it turns out!!