I am a manager of my company .I just could study my 70-646 materials over the part time.I thought I could not pass this exam just once .I had planned to take the second shot.So, I think nobody can not pass 70-646, if you learn your materials in the right way. Here I share my experience, which aims to help more and more people like you and me out.

Firstly ,the key to pass 70-646 is that I have chosen a good book for me to study .Although many materials related to 70-646 are popular on the internet ,such as MS press ,Sybex , CBT nuggets videos ,and so on, personally ,MS press Win Server Admin Book for 646 are best book for us to study the Windows Server 2008, Server Administrator .Because this self-paced training kit can help us maximize our performance on 70-646,which provided not only the study guide and practice tests on CD to help us assess our skills ,but also real-world case scenarios to help us build skills .More important , focusing on Windows Server 2008 Administration, the 646 self-paced training kit can help us better understand the main topic area and objectives .

So, you have chosen a good book. After studying the theory, you should do all the practice questions /tests in the MS press books, and do all the labs in a virtual server. I also used the Transcender practice tests, which cost $99, but I can’t enthusiastically recommend them. They delve into a very deep level of detail, bordering on minutiae, but I can’t say they were of any practical value in preparing for the exam. The MeasureUp exam included in the MS Press book was very good, however. So, don’t rely on some braindump materials .The mentioned materials have been best for your 70-646 preparation.

A piece of Advice for preparation MCTS 70-646:
If you’re preparing for 646, make sure you are familiar with all the new tools and technologies, how they are used, and what they can and can’t do. In choosing solutions, you’re sometimes presented with several choices which will work, but only one will be the best based on the scenario presented. So, know the pros and cons of the different ways to do things, such as cost, hardware resources required, effects on users, network bandwidth, etc.
I wouldn’t call the exam difficult, but I did spend about 6 weeks getting thoroughly familiar with Server 2008, not just to pass an exam, but to use it for the next 5 years or so. I think the exam was actually a little easier than some of the blistering ones I had in the 2000 & 2003 tracks. No complaints here!

Edit: How many questions are there in 70-646?

About 40 questions .Because 70-646 is a traditional question-based exams, there are no labs and just questions in the exam type.
How many scores you should get to pass the MCTS 70-646 exams? I think it is know to all to get 70% of the total scores. However, generally speaking, the total scores are 1000.
If some of us want to take online training resources for 70-646, the MS Classroom Training is enough for us.