How to setup a Backup Domain Controller

I have a server that I want to set up as a BDC. The PDC is called “Server” and has two hard disks. The first disk has two partitions C(2gig)& D(10gig), the second one has E(10gig) & free space of 10gig. The BDC has two hard disks also but have not yet been partitioned Whats the best way of setting up this server.