The international school that I went to offered AP classes because it was an American school. Considering it was a small international school it did offer quite a few AP courses such as: Calculus, History, English Literature, Physics, Chemistry, Biology, Human Geography, Economics and French.
Of these courses I took Calculus and Economics. Looking back at these courses I realize how much I enjoyed taking them. They were challenging courses, but challenging in such a way that provided me with a sense of fulfillment at the end of the day when I had finished my homework for Economics and figured out something about supply and demand, or had done some derivatives and gotten the right answer.
From what I have heard from various counselors and international admissions directors, the courses that you take do play a role in the decision process of the university admission agents. There is a balance here though. You have to understand that just taking a challenging AP/IB course is not enough, one has to do fairly good in it also. One has to show to the admission agents that it is looking for a challenge and that it is ready to take that challenge on. I got at least B+ on my AP courses which was good enough to get me into 7 out of 11 universities/colleges. If you know you are fairly good at a subject and want a more challenging course, it is a great addition to your admission file to have one or a few AP/IB courses on there. BUT, if you know that you will have trouble with that course and are unsure about getting a B in that class then it is probably wiser to drop out of that class because failing that class isnt to your advantage. It will bring down the GPA and show the admission agents that you are not quite ready for college (not ready for their college).
To the statements above there are always exceptions. If you know the professor that is teaching the course and you know you understand the way he teaches and that he is willing to help you out even after classes in order for you to succeed in that class, then by all means go for it. In my academic experience a great teacher could mean the difference between a C+ and an A. I had teachers that just were not meant to teach and then I had other where I time would go by so fast that I didnt realize the class was already over and I was eager to learn more.
It also depends on you how determined you are to do well and how much time you are going to devote to studying hard. If you keep practicing you will eventually get it and it will become second nature to you.
Thats why you really have to take some time to seriously think about your options and decisions you have to take and how those decisions will affect your admission chances.
Another thing about the AP/IB classes is that, if you end up taking them, you will have a much easier time in college when you have to take those courses because you already took them. It will be like a refresher for you and you and your parents will be very happy when at the end of the first year in college you bring home B+ and As proving that you have not fallen into the trap of binge drinking, sleepless nights and other good things that happen during your freshmen year in college. All because you just took some classes that you already took in high school.
Good luck on your admissions!