IT Employment

I have read the articles about migrating an NT to a W2k3, and migrating 5.5 to Exch 2k3. My plan gets cloudy because I want to do the following:
- Migrate NT to new domain. (abccorp to abc-egf.com)
- Migrate Exch 5.5 to Exch 2k3

What happens to Exchange 5.5 site? Is it possible to use the ADMT to move users to a new domain and still keep functionality with 5.5?
If it will work, what happens when I upgrade 5.5 to Exch2k3? Can I switch domains in the upgrade?

While I am doing this, I would like to take the opportunity to start the network as clean as possible. I want to change the doamin name to reflect a new company name. There are just these questions that I want to have answered during this planning stage instead of having to answer them during the migration. Any help you could give would be appreciated.