Chances to get accepted by Waseda Univeristy?

Well, I am interested in School of Political Science and Economics, Waseda University; however, I've heard that Waseda has a very high competition and those to got accepted get 2000+ for SAT score, is that true? Is it possible for an applicant, like me, to be accepted by the Univeristy with only 1600-1800 SAT score with GPA 3.58 ?

Glad you're interested in Waseda!

Are you applying to SPSE or SILS? That makes a great difference (not entirely practical, but you will have a different perspective). I'm in SPSE, as well as a resident of the WISH dorm, and I would advise you to STEER CLEAR of WISH dorm, first of all (I can go into detail, but you can google some complaints on yahoo answers if you're so inclined). The student body is what you make of it, but the teachers (non-mathematics) are excellent. Without considering the quality of professors, Waseda is a university struggling (relative to, say the top Ivy Leagues, in terms of recognition), but is indisputably STRONG in Japan, comparable to Tokyo University for its employability  especially SPSE). Dislcaimer: My views are mostly from SPSE, and what I know of SILS are from friends and so on.

Also, it's highly recommended to join a circle for socializing, with clubs being more intense. You may or may not find it to be your thing.

As for likely the biggest concern in your mind (as it damn sure was for me and many who have asked me): How competitive are you? I'll offer you some advice, but as much as I would like to predict your chances, I'm no genie and I'm definitely not fit to be one.

That said, here are my tips:
1) Bolster your SAT (I believe Japanese schools tend to grant greater value to standardized scores). Even if it'll be hard to take another one, do it anyway. Study like hell. If you luckily have more time you can even go the shotgun method and retake the SAT (though it has changed since I've taken it, the test is still fundamentally nearly the same).
2) Make your essay damn good. Follow the rules: A4, word limit, etc...
3) Picture yourself at the entrance ceremony with a two-piece suit (assuming you are male), as the directors make their opening addresses and sing the Waseda school anthem.

Wase... Wase... Waseda...

Best of luck for admissions!

P.S. Where did you hear the 2k+ SAT acceptance rate? There are plenty of people who enter (albeit conditional offers) with scores a few hundred points lower.