Users Profile migration

Hi all,

we are inplace to migrate from windows nt to windows 2000 AD . the old setting has the domain name include _ character , and the new ADC will be with new netbios name. our enviroment include more than 3000 users 1000 of them has xp and 2000 pro. my question is how to keep or migrate the users profile to the new enviroment .
when the user login to the new domain they will lose theire profiles and outlook setting .
is there any way to keep or migrate users profiles