How to add proxy addresses in Exchange 2007   

Hi
How do I use the set-mailbox cmdlet to set X500 addresses (proxy addresses)

I want to use a script to set this for a lot of users.
I will be using an import file containg the user and their x500 address.

These are for mailboxes that have been migrated from Exchange 2003 to 
Exchange 2007 using PSTs using export and import.

Want the old DNs.

Thanks

date: Thu, 1 May 2008 09:13:44 +1200   author:   Dummy