You can have single card multiplayer according to IGN.
IGN AU said:
having one-card / four player games is excellent. We really appreciate being able to have a couple of friends around for a bash, or have a two-player game on one of the included puzzle games specifically tailored to two players.
Mario Party DS has full-featured single-cartridge multiplayer support where the whole game can be played with four players with only one copy of the game, and utilizing the Nintendo DS system's Download Play feature. Though the initial load time is a little long and there are bits of load screens throughout the experience, the developers did a fine job hiding a lot of the loading from the host system to keep the pauses between the board game and mini-games as minimal as possible. Nearly every aspect of the Mario Party experience is translated into the single cartridge environment, and we thank Hudson for getting this working smoothly…Mario Party needs multiple players to be good.
