[luckieluuk]

All you'll need is just some (not too) old pc (or laptop, they work great when talking about electricity costs) wich might even be able running Linux Server Edition (or just the desktop version) and for the internet connection was for 100 players 4Mbps upstream required (according to Wiki) Also you'll need a good router (if u use any) wich u can configure to port forward (I suggest you can find that yourself on the internet or the routers manual)

All you'll need then is: www.whatismyip.com and pubish your IP with server ports to the world somewhere :P And you can play.