If you have received an email that another account has granted you access to their inbox, you need to click on the link to accept the share. Once you've done that, here's how you open the inbox in Outlook:
- Click Start > All Programs
- Click Google Apps Sync 2.0 > Add account for delegation
- Enter the email address of the account that was shared with you
- Click OK
- The inbox will now show up in your Outlook folder list.