Not done it, but I would strongly suggest getting a virtual machine up and running with Exchange 2007 on as it is very different to Exchange 2003. (Unlike 2003 which was very similar to 2000)
Prefer Exchange 2007 to 2003 it's just easier.
And once the setup is done you should be able to do everything user related from the AD (obviously with Server 2008).
The only niggle I have is that on 2003 all the users have to be setup in it and it's no the quickest of things to do.
M.
I've sat 70-236, 70-237 and 70-238, only passed the last two though. As far as exams go they are like any other MS exam in format. I used TechNet and MSExchange.org for resources (there was no publications as I took the exams in beta form).
Any questions and i'll try and answer them without breaking the NDA.
Sorry mate think you mis-read. I was referring to Server 2008 where you will be able to manage them using the AD. Currently in 2003 you can't do this.
M.
Okay Powershell is the underlying foundation of the Exchange GUI so anything you do in the GUI you can do with cmdlets. I would STRONGLY suggest you pay particular attention to these.
With regards to what to study all I can say is follow the preparation guide:
http://www.microsoft.com/learning/en/us/exams/70-236.mspx