, download whichever one that will work with your OS and install as non-commercial license(free!).
Run Hamachi, go through the first time helper, then click connect>Join existing network, name and password is "McNinja's VLAN" and "nerts".
Hope someone else has done this, or it's just you and me. =P
You're tricking your computer into thinking it's on a LAN with everyone else on this network, making it way easier to set up games between crazies, especially on older games that usually require you to know someone's IP.
This should go without saying, but don't use this to fuck with anyone else's computer.