They need to give you permissions to view it (either as a delegate or using
folder permissions), then you use file, open, other users folder. http://www.slipstick.com/outlook/otherusers.htm
http://www.slipstick.com/outlook/sharesubfolder.asp has instructions for
giving folder permissions. If the folder is a default folder, you can use
the open shared folders link or file, open. If it’s a subfolder, you need to
add the mailbox to the profile.