|Assuming that you are not still running NT (in whch case why is this post in the 2012 forum?) there are no such things as primary and secondary DCs. Exactly what advice do you need? You just set up both machines as DCs.|
Hardware-wise, i would use RAID-5 and have dual PSUs and NICs in each server, teaming the NICs for redundancy. But with dual DCs you don't really need to worry so much about hardware redundancy.