Word is coming through that the popular German magazine, Games Aktuell, will have the first details on GTA 4's mutliplayer system in their next issue. The issue is due to go on sale on March 19th, so expect more information around them. GTA IV will feature multiplayer game modes called "Team Deathmatch", "Cops n' Crooks", "Deal Breaker", "Bomb da Base" and "Hangman's Noose", amongst others which we hope to learn about soon. We understand that the magazine got to play two of these modes.
Related Link: GTAForums Topic.