tasks in shared project

I’m having trouble trying to figure out how tasks work in a shared project. What I want to do is share a grocery list. I can access it on my blackberry and my wife can access it on her iPhone. The problem I’m having is that anything she creates I can’t see and anything I create she can’t see.
Part of the problem seems to involve the assigning of tasks. Is there anyway to see a task that is not assigned to you. If I assign a task to her through the website, it is immediately gone from my view and tasks that she created, she is unable to see. I’m on a Mac, she’s using XP. Any ideas??