I kept running into trouble when trying to add a second Exchange account to Outlook but Tim M. to the rescue.
Here are his instructions for another email account on the same exchange server:
Configure Outlook to display that inbox all the time, in Outlook 2007 it’s Tools -> Account Settings -> Microsoft Exchange Server -> Change -> More Settings -> Advanced -> Add -> new_account_name. OK OK OK OK OK OK and maybe OK.
Whee hew! Worked like a charm.
Note: this is only for reading emails from another account not creating a separate inbox or sending accounts.