The huge LAN on the picture (http://www.lanparty.com/pics/index.asp?id=234658) is The Gathering 99, arranged every easter. It is, in fact, the world's largest temporary Local Area Network. Their upper limit is 4500, with crew there are about 5000 people in the arena.
The arena, by the way, is located outside Hamar, Norway.
The Gathering is not primarily a gaming party, although it has become more of that lately. The demo scene does also gather at The Gathering, and their excellent productions make the party memorable.
For the 2001 version of the party, they sold 2500 tickets in less than 24 hours. Black market tickets at the major online auction houses are now at three times the real price - and they have 1500 normal tickets left to sell (they just haven't done so yet).
The feeling of being at The Gathering is amazing! 4500 people in 120 hours (that is 5 days and nights)...