I am an unltra-newbie, help needed.

Hey all. I really want to play Call of Duty online with my brother but we both have the same CD-key, so we can't join the same online CoD server. I decided to try tunneling software, and I was pointed to GIT.
But how do I use GIT??
I read the readme but I am still pretty confused. If anyone has the time I would very much appreciate a walk-through for setting one computer as a server and finding/connecting to this server from another computer. Once the virtual/fake LAN is set up, I know what to do.
Both me and my brother are running WinXP Pro. Both of us know very little about networking, especially this tunneling business.
Thanks for any help.
But how do I use GIT??
I read the readme but I am still pretty confused. If anyone has the time I would very much appreciate a walk-through for setting one computer as a server and finding/connecting to this server from another computer. Once the virtual/fake LAN is set up, I know what to do.
Both me and my brother are running WinXP Pro. Both of us know very little about networking, especially this tunneling business.
Thanks for any help.