I actually just graduated from Carnegie Mellon -- Thanks BerkeleyPreMed for all of those comments, as CMU is somewhat of an underdog. Anways, I thought I would share some of my own experiences there to help you decide.
First of all, I loved being a student there. You work your butt off, but you get such a great education...in the class room. Problem that I had was that the whole student body always seemed so stressed out, so overworked, that it kind of lead to a less than desirable social atmosphere...which is just as important. What I would do is check out the activities and extracurriculars that are available at CMU and decide whether any of them seem suitable to your interests. You can find this on their website. There were really only a few that I found appealing, and so my extracurriculars more or less involved a lot of research (big research school!) and a little tutoring with disadvantaged kids. Since you are playing football, that may quite possibly serve as your best social outlet.
In terms of academics, everything BerkeleyPremed said is right on. But now do you want to major in computer science, physics, engineering, or cognitive science? I believe you said something about international politics or economics. CMU does not have an international politics department, so you would have to do a self-defined major (which is possible, I know many people who have done it). They have economics, but just be warned that CMU is known for being a "tech" school, so everything has a "quantitative" spin to it. If you really enjoy liberal arts in the very traditional sense of the word, then liberal arts at CMU is probably not right for you. Also, you would have to determine whether you could take classes at Mellon College of Science, as your major would be in the Humanities College (you apply to separate colleges at CMU, you're not just admitted to the University at large).
One last thing. CMU sciences are HARD. People in that college work their ***** off, and don't look like they're having a lot of fun. Also, I don't think our record for getting people into medical schools is that strong. I would really pay attention to that as you decide. Although I can't speak from experience (I wasn't premed at CMU), I don't think that professors there are into the whole medical school thing. I feel like professors there push the PhD route instead. Maybe I get that feeling because the school is not associated with a medical school and so the professors aren't influenced by it, and they're mainly involved in research and more "techy" things. I don't know. But I know that the "softer" science professors are few and far between. So you will have a lot of fun finding that OChem or Physics Professor who is most likely to give students some slack and not be a hardass just for the sake of it. Truth is, they're interested that you learn, but not necessarily that your grades reflect that. Most of them could care less.
Also, considering you are going to be an athlete, I must forewarn you that CMU is not an incredibly spirited university. I think we have pride in our school, but athletics is not the center of too many people's attention there. I would attend one of the sporting events just to see how many people show up. You may be surprised! So if a big crowd cheering you on makes the sport more fun, I wouldn't go to CMU.
I hope this helps. If you have any other questions please feel free to ask. I worked in admissions my first two years of college so I don't mind taking on that role again. Also, I know a lot of this may sound negative, but CMU is,at least in my opinion, for a very particular person. And really, deep down, I don't think it's the right place for a PreMed. The social scene (not the same as party scene...) is not always healthy, and I think that is very important to cultivating those interpersonal strengths that are so important to being a good doctor. Not that your individual social competences won't prevail, it's just not the ideal situation.