Sorry to disappoint you on two fronts, but not only can you not play Maul, but your friend is a lyin' fool
Seriously...you can't play Maul in either PC or Playstation versions. Your friend might be talking about Jedi Power Battles, in which you can play as Maul, I believe only when you complete the game. Maul was considered as a playable character, but we ran outta time.
Hmmm..perhaps I should build a Darth Maul model so that your friend can eat crow