pentejr, alanback: The way they work is that the players are ordered by rating and the list split at the midpoint. The players on the two list sare then matched against each other. In an 8-player tourney, for instance, it would be 1-5, 2-6, 3-7, 4-8. This prevents the lions from killing each other too early in the game.
At Vog, where any number of players are allowed into these tournaments, not just a power of two, there is a bye for the top 2^whatever players and the very lowest rated must play to get through to the second round. Because the topmost players have had this bye and are in the second round they will then be paired 1-2, 3-4, etc, even though it's their first match of the tourney. (That's just to let you know how it works elsewhere should you encounter it. There are only power-of-two sized tourneys here, so that situation doesn't arise.)