XFire and Gamespy would be great, Steam would be absolutely fantastical. If you haven't already, maybe see if you can get in contact with them to see if something can be worked out.
Also, you don't necessarily need to completely know the person, just make sure you set some times up when you'll meet before you finish each session, and be sure that you stick to it.
On that note, Zul, I'll be on at around 2pm until around 7pm to finish up that game. Check the IRC for me and I should be there.