Here are the steps that i take to get an organization from 2003 to 2007 and 3.5 to 4.0

1. Import business organization
2. Import Business Organization Users
3. Subscribe the Business Organization to hosted e-mail
4. Assign available user e-mail plans
5. Import SMTP domains
6. Move mailboxes (exchange management console)
7. Import mailbox for every user
8. Delete OAB /GAL / AL
9. Manualy delete GAL using ex2003 system manger
10. CreateAddreslists
11. EnsureAdresslistStamp

xml's for task 1 and 2 can be found in the Hosted Active Directory Import folder

xml's for task 3 and 4 can be found in the Hosted Email 2007 folder 

All the xml's for the tasks 5 - 11 can be found in the Hosted Email 2007 Import folder

Hope it helps.