i passed the test 406 2 weeks back, its not very tough if you have already worked with websphere before. thats encouragement
to answer your questions now,
1) the answer your prometric rep has given is basically right, you have 55 questions and 75 min time(roughly) and you need 50% to pass so that makes about 28 or lets say 30 questions to pass.
2) well ibm does say that you need to get 50% to pass
3) you can go to 2test.com and register, thats what i did and i had no problem what so ever
4) the 2 books you have are the ones that are prescribed for that test, you need to go through both of them. other than that go through the infocenter, thats one of the good references.
now after that there is the practice test on the ibm site, take that test many times about a week before the exam that should give you a basic idea of how the test goes.
get the servlet API thoroughly, there are quite a few misleading questions
that you can answer only if you have that API at your finger tips.
and finally all the best, all said and done its not a very difficult nut to crack. you can do it