Open a Shared Calendar using Outlook Web Access (OWA) for Exchange 2003 (Please note that this option is not available in Exchange 2007)

If someone has shared their calendar with you, you can access it via Outlook Web Access.

1.  Log into Outlook Web Access

2.  Once your mailbox is open, go to the address bar in Internet Explorer and add

                         /username@domain.ext/calendar

     to the end of the line. 

As an example, Amy@mymail.com has given permissions to her calendar to Alexander@mymail.com. 
Alexander logs into OWA and gets to his home screen.  His address bar will show something like:

        https://ex14.myhostedexchange.com/exchange

To view Amy's calendar, he would change the address bar to read

        https://ex14.myhostedexchange.com/exchange/amy@mymail.com/calendar

To return to his mailbox, he would simply remove the amy@mymail.com/calendar from the address bar and hit enter.

Note:  This article also applies to shared contacts and inbox.  The difference is that instead of /calendar,  you would type in /contacts or /inbox, depending on what you want to access.