Thanks for your replys.

To Martin Honnen,
  Yes, the server support JSP. So, do you mean JSP is a good choice
and not necessary to mix use of other language?

To Andy Dingley,
  about the quantity of the students and tests. The test should be
about 10 questions per chapter, and mayb about 10 chapters. I am not
quite sure about the quantity of the students. r u considering the
load of the server if i use JSP? so, how many users u think are big
load for the server (university server)?
  about XML & database. why u say "don't store all tests in the same
XML file"?
so, do u prefer 1 chapter one file?
And, i do want to put all the information within one
<question></question> element, including questiontext, possibleanswer,
and correct answer. any problem with this?

And, 
To all of you,
I worry about if the users (with different Browser and different
operating system) can access my webpage.
I know IE support about XML. I made a page that implements one
question in the test (with JavaScript & DOM, again, is that not good
to mix use of the language?). It can display in IE,but not in Netscape
or Opera. As you r a developer, should u consider this problem
(different browser) is that important? or, just make one suit for IE
is enough?

To Gerald Aichholzer,
  Apache Cocoon is quite new to me. and i don't want to spend much
time to study this new staff. Anyway , thank u very much.