I am in the process of getting ready to migrate off of Exchange 5.5
SP4 to a newer version on a new server

My environment consists of multiple NT.4.0 servers and Win2K servers
so I am not running active directory yet.

I am not sure if I should go straight to 2003 or stop at 2000. Is one
migration path easier and less vulnerable than the other??

Can someone point me to a best practice document or offer any ideas

Thanks in advance