I currently have the ACDT, ACPT, ACTC 10.2, and the ACHDS cert. I am currently working on the 9L0-505 for my ACTC 10.3.
The best teacher I have found is experience. I use the Apple Skills Assessment guides and the pdf's provided by Apple for the server technologies:http://www.apple.com/server/documentation/
There are only a limited number of books out there and online test prep is pretty scarce. I also work for an Apple Authorized Service Provider and get access to training for the ACDT, ACPT and some server stuff, but not enough to pass the ACTC exams. MacAcademy has some CBT based courses that are very good, they do have a course for 10.2 server, but not 10.3.http://www.macacademy.com/indexwin.html
I have found the Comptia exams easy, the Microsoft exam I took was one of the toughest. The Apple server exams are difficult without the right preparation. There are alot of "choose all that apply" questions. The exams really test you on what you know, not just to see if you memorize the answers.