The simplest way to find the DC's (Domain Controllers) is to use the 'nltest' utility from the resource kit for the OS that you will be using to make the query - just google for 'nltest' and your host OS, though they are usually on the Windows CD.
Once you have nltest, assuming you are looking for the 'EXAMPLE' domain:
Find all DC's : nltest.exe /dclist:example
Find primary DC : nltest.exe /dcname:example
It has a ton of other options, go play