Should I take the 2004 test or should I wait for the 2005 test?
This depends on your current preparedness level. If you are already prepared for the 2004 test, I suggest you to go and take the 2004 test, before 24th September. For that you will have to apply before 29th August 2004. Two months is enough time to prepare and pass the exam.
If you are just starting your preparations, then my suggestion is to start the preparation with PMBOK third edition. What is the point in going with a knowledge base, which is being replaced with a fresh set immediately. There is not much of a difference in subject areas between PMBOK third edition and the earlier version, except that PMBOK third edition has more clarity and some more best practices are incorporated. Start your preparations, based on PMBOK third edition, by around 25th August 2005 take stock of your confidence level and if you are confident, go ahead and apply for the 2004 test, before 29th August 2005 and take the test before 30th September.
In case you are not very confident about your preparedness for the exam by around 25th August 2005, don't worry. Your preparation is not wasted, since it is based on the third edition. It is only a matter of some more preparation, before you attempt the 2005 examination.