The concept behind Xbox LIve, Bob, is a bit different from what you may be used to with PC multiplayer. There are no servers - per se. When players join up for a game, the system automatically assigns one player's Xbox (usually the one with the best connection speed) the role of "host." This has advantages and disadvantages, most of which I'm too technically illiterate to explain.
However, Live is more player-centric, than server-centric. So unless you have people in your Friends List who are playing the game, you really won't be able to browse. This makes it much, much easier to protect the "integrity" of your game - by preventing random folks from popping in (or even seeing yoru game), but can make it hard to find a game when you don't have many friends.
It's your standard Console vs. PC type of thing, but having been a staunch PC Games supporter for many, many years, I have to admit that the seamlessness of the experience has swayed me.
