Solitaire Showdown
MSN Messenger 6 contains this game (in the Launch Site menu), based on the original Solitaire in Windows. It is online, 2 player, and features 2 decks. Each player must race to put their cards on the shared pile (e.g. putting an ace of any suit on the pile, but putting 2's of a suit may only be possible after the ace of the suit is currently on the pile, not covered by any other cards).