I just completed this project here. The best way I found to do this is to bring up a “Pivot server”, something that is big enough to handle your domain for a week or so. Bring that server up as a BDC in NT4 fully updated. Let it sit for a few day to make sure it is working. Then promote it to a PDC (this will demote the existing PDC). One thing, you need to make sure that if your current PDC is doing DNS, WINS, DHCP… that you transfer those over to the new pivot box. Once you have it promote let it sit for a week or so and watch the error logs. Make sure everything is working right. Then take your server 2003 CD and perform a upgrade on it. This will take about 2-3 hours so make sure to do it at night or on a weekend. Everything else you can do during the day as long as you know your settings are right. Once you have it upgraded let it run for a few days again and watch the error logs. Once you are sure that it is working turn on your new server running 2003 and add it to the domain as a new dc in an existing forest. Then run dcpromo on it to promote it to the main DC. You’ll need to turn on global catalog on it also. This should transfer all setting over to the new box. Once everything is replicated you can run dcpromo on the pivot box and remove it. One thing to note: buy a tool called upromote. You need to buy the old PDC NT server back to a standalone before you can remove it form the domain (unless your new server will not have the same name, in this case never mind). Hope this helps. Take a look at Microsoft’s site. They have a big doc for doing this.