Migrating Windows NT 4 to Windows 2000

I have an nt 4 network (with 1pdc, 3bdc and 1 member server) with a domain name MIS. i plan to migrate to windows 2000 and was told that i need to have a domain name such as MIS.COM and not just MIS.
On all the client computers9windows XP pro, 2000 pro and 98) I have the network setup with MIS as the domain name. To change the domain name of over 200 xp/2000 pro clients means a lot of work especially the copying of profiles.
What is the best solution to achieve this or can I still go ahead to use MIS as the domain name in Windows 2000 server network.