To open another person's calendar you have to know a name Outlook/Exchange can resolve. The format which seems to work best is "Lastname, Firstname":
Some basic code to fetch these entries might look something like that:
using Outlook = Microsoft.Office.Interop.Outlook;
/* ... */
// Login to Outlook and exchange
Outlook.Application outlook = new Outlook.Application();
Outlook.NameSpace mapi = outlook.GetNamespace("mapi");
mapi.Logon(null, null, true, true);
// Resolve the user
Outlook.Recipient rcp = mapi.CreateRecipient("Lastname, Firstname");
if (!rcp.Resolve())
{
// Error handling - User not found!
}
// Get the calendar folder
Outlook.MAPIFolder calendar = mapi.GetSharedDefaultFolder(rcp, Outlook.OlDefaultFolders.olFolderCalendar);