There are many third-party vendors that produce NT to Active Directory migration tools, including the company I work for. You should do an exhaustive evaluation based on the criteria important to your purchasing decisions, should you go down the third-party route.
On the Exchange migration, again you will need either ExMerge from Microsoft (free), or Intra-Org, which uses the Active Directory Connector (ADC) and places the Exchange 2003 server in the Exchange 5.5 site. Or, you can do an Inter-Org migration, which is definitely best done with some third-party tools.
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This was first published in October 2005