Insomnia 51 (also known as i51) is an upcoming Halo 3 event which will take place on April 19th and 20th for European players to crown the Halo 3 Spring European Champions.
Players will be required to own a copy of Halo 3: ODST (for the Halo 3 Mythic disc), a wired headset and a wired controller.
Prize Pool1st Place• 4 x Vibration Headset XTs
• 4 x Twin Docking Stations
• 4 x Twin Battery Packs
• 4 x Poly bagged HDMI
• 4 x ROXIO Game Capture HD Pros
2nd & 3rd Place• 4 x VX Comms Elite Headset
• 4 x Twin Docking Stations
• 4 x Poly bagged HDMI

You can get more information about i51 including the location of the venue and where to purchase tickets
here.