My understanding is that if you set up the new email to divert before it arrives at Outlook it will appear as if it is the from existing address but you will only be able to send from the existing address and not the new one. Alternatively have the new address delivered to Outlook and run 2 e-mail addresses from Outlook. I have 4 e-mail addresses arriving into Outlook.
BTW which version Outlook and confirm it is not Outlook Express. Same applies though.