Based on the newly launched Grand Theft Auto IV web site, we know that the game has some sort of multiplayer component. What we don't know for sure is what it involves. But according to a rumored tagged report from Destructoid, citing an anonymous source, a suite of multiplayer options are planned, including death match, co-op, team based head-to-head battles and online races. While that may sound like a list of vague concepts that could be just an educated guess, the site's source has names for each, including Cops 'n' Crooks, Bomb da Base and Hangman's Noose.
If true, it would be the first Grand Theft Auto title to feature such a significant multiplayer aspect to the game. Check out the full report for more info on rumored multiplayer additions, including a look at some of GTA IV's side quests and mini-games.