sharing email inbox

> my computer is running XP pro, and is being used by a
> family of three, two users, and one adminisrator, we
> share the same ISP, and the same email, we all use
> Outlook express, If one family member logs on to the
> computer using thier own identity, and then checks email,
> the messages they download can not be viewed by the
> others if they log on under thier own identity.
> I need to be able to share the inbox and outbox with all
> users. does anyone have a solution for this.
> Thanks
> David