A quick one Ferrovasi (as a WoW and 4e player - they are nothing alike ... at all).
Take up inexorabletruth's offer of joining one of his (or dReaper's) "newbie" games, they will try and not kill you and help you along the way. Once you have played one of their games, jump on in to the Game Ads and join a game (and as IET has stated, pick a system, either 3.5, Pathfinder (my favourite) or 4.5 to play) and join one of the games.
Getting picked for the game is harder then being in the game as you'll notice (you could go and look at some now if you wanted) people put an amazing amount of effort into their character's background, personality, goals, etc.
Generally once the GM has got a mix of peeps he likes, it is only then that the mechanics of the game come into it (it doesn't matter if your halfling rogue is a 3.5, PF or 4e character until the game starts) -- the GM will stat what game system they are using in the add obviously.
Good luck and see you around the web,