Generally, US medical schools don't or very rarely accept non-US undergrad. degrees. They're especially picky when it comes to the premed req's. Some (Columbia/Harvard comes to mind) explicitly states that your prereq's must be from an accredited US institution. Don't know if you can get around it by taking a post-bacc., but it'll certainly be an uphill battle. Also note that you're likely to run into visa issues. There shouldn't be a huge problem getting a student visa, but you'd need a work permit for residency.
To top it all off, you can't get federal loans to finance your education if you're a non-citizen, and a large number of other financing options would also be closed for you. In fact, you can't even get research support from NIH (if you want to become a researcher) without a green card or citizenship.