The other day at work I needed to upgrade the functional level of the AD Forest from Windows 2000 to 2003 R2. I was going to add another server and make it the main AD server. It is running 2003 R2 but the rest in the domain controllers are running 2003 RTM with service pack 2 of course. Anyway, from what I remembered, upgrading the level would not be a rebootable procedure but I could not find absolute proof even on Microsoft’s technet site. I proceeded to do every check in the book that I could to make sure that AD was working great. Everything checked out and so I went and upgraded it to plain ol’ 2003 first. On a side note, the domain level was already 2003. After that I had to use the second CD that came with 2003 R2 and run the ‘adprep /forestprep’ on the schema master. It made me a little nervous but it worked fine and still no reboots were required which I was thankful for and expected but with Microsoft you don’t always know. Just make sure you run the adprep command from the Schema Master. That part is important to the success of the upgrade. After that I was able to install AD on the new server. With Windows 2003 R2 the adprep command is located on the second CD in the path of ‘CMPNENTS\R2\ADPREP’.