Usually to play multiplayer games more than 4 joypads on your game console you should connect two or more consoles together with a network cable in the same room or connect your console to the internet and pay for a matchmaking service.
Xlink Kai is a tunneling software for Windows that allows you to create a direct connection between two or more identical game consoles through internet. Originally created for Microsoft original Xbox, it now supports Xbox 360, Nintendo Gamecube,Sony Playstation 2 and Playstation Portable.
It works fooling game consoles, in other words making them believe they are in the same network the other console is, to achieve this it requires you to connect your console to the same network router or switch where your PC is connected to internet, then let the software web interface detect your console.
Unfortunately you wont be able to play all multiplayer games available for your console, only those games that support "system link" can be used with Kai, mostly because those allows you to wait on a "lobby" for the other user to join your room, thats when kai comes to the rescue!
The initial web setup could be complicated for the average pc user but once you are done, it really easy to find or create virtual rooms to play in Xlink web interface.