nt 4 .0 server pdc

Hi
You cannot have more than 1 PDC for a domain. You can have as many BDC's as you want but that should be according to your requirement depending on the number of users who are going to login to the domain. Otherwise it may be waste of resources. In normal circumstances you can promote a BDC to PDC from the Server Manager. At the moment when all the DCs should be on so that all the servers synchronize while doing so and will know which server will be PDC after promtion. In this process the previous PDC will be automatically demoted to a BDC.
Thanks & Best of Luck

Just throwing in my 3 cents to this...
1 PDC per domain (that's why its called a PDC -- PRIMARY domain controller).

You can have as many BDCs as limited, as the other folks pointed out -- however unless you are huge you are doing nothing but wasting resulting and creating more vulnerable security points in your network (every domain controller is a potential "door" into your network, people who want to get into a network know this of course and they will "probe" for DCs and then attack them first usually (webservers are another "juicy" target on any network)). Anyway considering a BDC can "by the book" support upto 2500 nodes/accounts, unless you are huge company with literally thousands upon thousands of employee's -- there is no real need for more than one BDC.

Hope this helps.

laters.