Their forum: http://www.artofproblemsolving.com/Forum/index.php?

]]>Patternman, I did so quite a few of them before going to university.

]]>Assuming you mean the International Mathematics Olympiad, obviously you should start of by learning the material for it, which is algebra II, combinatorics, number theory and precalculus (elementary functions). You can use calculus on them, but they are designed to be able to be solved without using calculus. After that, i suggest you do as many challenging problems as you can find. That's basically what I did, and now I am in a position to solve most IMO problems with ease. Just remember that knowing the prerequisite material is not enough - you need to have problem solving skills, creativity and ingenuity - all of which comes by solving difficult problems.

That sounds impressive that you can do most of them with ease. Did you ever do them before going to college/university?

]]>