migration to 2000

migration to 2000
i have an nt4 platform /pdc and bdc with exchange 5.5 and a proxy. users aprox 200. migrating to 2000 sever with active directory seems to be my focus for transition..I would like to know if migrating all the permissions, users and settings is a best bet or to start from scratch with a full install instead and reconfigure all previous info.. i ideally want to have to identical severs for complete redundancy any comments?