NT4 to W2K Migration

I am planning on migrating our NT4 environment to W2K\Active Directory. Can anyone suggest the best way for me to do this – I would like the setup to be as follows: One domain under which there are 3 different sections representing 3 departments (which are currently separated domains) – I’m not sure if these need to be sites or child domains within the Active Directory environment? The departments will contain there own servers – does this mean that all 3 departments will have main domain controllers? Please put me in the right direction – ideas, good web links, etc. Thank you.