Access Exchange email of another user

Hi
I’ve been given Admin rights in a small company and my senior asked me to set up a way for the two of us to access each others emails from our own computers if one of us was to be sick.
I had OWA in mind, but that can only be used outside the network…?
I’m no Exchange guru, so I’m not a 100% sure.
server 2003, Exchange 2003, XP workstations.
What other options can I use to do this.
Thanx