Exchange 5.5 to 2000

I am planning on upgrading from 5.5 to 2000 with the following method, will this work?

5.5 is currently on my NT4 PDC, I have a BDC in place. I will upgrade PDC to Windows 2000. Promote my BDC to PDC. Then do an in place upgrade of 5.5 to 2000. Do I need to convert everything to active directory fo this to work? Can I just keep my NT 4 domain? What problems might arise?