disabled accounts

When migrating to a new organization,from 5.5 to exchange 2000, the account is disabled. can we enable the account? and why can I not do a 2 way connection agreement when in mixed mode?I have created a test site that is in it’s own work group, not on the wire. I am trying to migrate with MS migration tool from 5.5 to 2000. They are 2 different org. I am having trouble when after the migration of a users mailbox, I enable the mailbox on the 2000 side, then when I go back to the NT side I try to send an email to the old address of the migrated user and it does not forward the mail to the new location. I have set SMTP on both sides and A records and MX records. Can you help?